Merge pull request #110 from kristianwind/mcp-oauth

MCP: forbind med kontoen i stedet for med et token

docs/mcp.md

@@ -12,39 +12,70 @@ conversation.
 
 ## Connecting it
 
-**Make a token** under **Settings → API tokens**. The page then shows the
-connector address to go with it — token and all — which is the thing to copy:
+**Add the connector** in Claude with your instance's address followed by `/mcp`,
+and nothing else:
 
 ```
-https://todo.example.dk/mcp?key=vrd_…
+https://todo.example.dk/mcp
 ```
 
-**Add the connector** in Claude with that address, and nothing else. The dialog
-asks for a name and a URL; leave the OAuth fields empty.
+Claude sends you to verdande to sign in — the ordinary sign-in, passkey and
+second factor included — and then asks one question: *"Claude wants to connect
+to your account"*. Press **Allow** and you are connected. Leave the dialog's
+OAuth client fields empty; Claude registers itself.
 
-!!! note "Why the key is in the address"
-    The dialog has no field for a bearer token — only OAuth client credentials —
-    so a header cannot be configured from it. The address *is* the credential
-    here, exactly as it is for the [calendar feed](caldav.md#subscribing-to-a-feed).
-    Treat it like a password: anyone holding it reaches what you reach. The
-    server logs request paths without their query strings, so it does not end up
-    in the log.
+The approval screen shows two things: the name the program gave itself, and
+**where the access is sent**. Any program can call itself Claude; only Claude is
+answered at `claude.ai`. If that line says something you do not recognise, press
+**Deny**.
 
 !!! warning "It has to be reachable from the internet"
     Claude connects from Anthropic's side, not from your browser. An instance only
     reachable on your LAN or over a VPN cannot be used this way.
 
+### With a token in the address instead
+
+A client that cannot sign in can be given a token in the address. **Make a token**
+under **Settings → API tokens**; the page then shows the address to go with it:
+
+```
+https://todo.example.dk/mcp?key=vrd_…
+```
+
+Treat that address like a password: anyone holding it reaches what you reach. The
+server logs request paths without their query strings, so it does not end up in
+the log.
+
 ### With a header instead
 
-Anything that *can* send a header should, and use the API path:
+Anything that *can* send a header should:
 
 ```bash
 curl -H "Authorization: Bearer vrd_…" \
   -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}' \
-  https://todo.example.dk/api/v1/mcp
+  https://todo.example.dk/mcp
 ```
 
-Both endpoints run the same server and reach the same things.
+`/api/v1/mcp` answers the same way. Both run the same server and reach the same
+things.
+
+### How the sign-in works
+
+verdande is its own OAuth authorization server, for MCP clients only — the shape
+the MCP specification asks for:
+
+- `/.well-known/oauth-protected-resource/mcp` and
+  `/.well-known/oauth-authorization-server` say where to sign in. An unsigned
+  request to `/mcp` is answered 401 with a `WWW-Authenticate` header pointing at
+  the first.
+- Clients register themselves at `/oauth/register`. Public clients only: a program
+  running somewhere else cannot keep a secret, so PKCE (S256) is the proof
+  instead. A registration nobody approves is removed after a day.
+- The code a client gets back is good for one minute and one exchange.
+- What it is exchanged for is an ordinary personal API token. No refresh token and
+  no expiry: it is listed under **Settings → API tokens** with the client's name,
+  marked *connected with your account*, and connecting the same client again
+  replaces it rather than adding another.
 
 ## What Claude can do
 
@@ -56,6 +87,9 @@ Both endpoints run the same server and reach the same things.
 | `update_task` | Change a title, priority, date or project. |
 | `complete_task` | Tick one off. |
 | `add_comment` | Comment on a task. |
+| `search_notes` | Find notes by text. |
+| `create_note` | Write a note, as Markdown. |
+| `update_note` | Change a note. |
 
 `create_task` prefers natural language, so *"add file the VAT return tomorrow at
 10am p1 #Accounts"* goes through the same parser the app uses — dates, priorities,
@@ -71,8 +105,10 @@ scope to configure.
 ## What it cannot do
 
 Delete projects, manage members, change settings or read another account. The tools
-are the six above; there is no general escape hatch.
+are the nine above; there is no general escape hatch.
 
 !!! note "Revoking it"
-    **Settings → API tokens**, delete the token. The connector stops working
-    immediately, and nothing else about your account is affected.
+    **Settings → API tokens**, delete the token — a connection made by signing in
+    is listed there under the program's name. The connector stops working
+    immediately, and asks you to sign in again the next time it is used. Nothing
+    else about your account is affected.

docs/openapi.yaml

@@ -3965,6 +3965,61 @@ paths:
         "422": { $ref: "#/components/responses/Validation" }
         "502": { $ref: "#/components/responses/Upstream" }
 
+  /api/v1/oauth/request:
+    get:
+      tags: [integrations]
+      summary: What the approval page is approving.
+      description: |
+        Takes the `/oauth/authorize` query unchanged. Answers with the client's
+        self-declared name and the host the code will be sent to — the part a
+        client cannot misstate. Needs a session.
+      security:
+        - session: []
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  client_name: { type: string }
+                  redirect_to: { type: string, example: claude.ai }
+        "400": { $ref: "#/components/responses/BadRequest" }
+        "403": { $ref: "#/components/responses/Forbidden" }
+
+  /api/v1/oauth/approve:
+    post:
+      tags: [integrations]
+      summary: Approve or refuse a connection.
+      description: |
+        Needs a session — a token cannot approve, or one leaked token could
+        mint others that outlive its revocation. Answers with the address to
+        send the browser to: the client's, with `code` or `error=access_denied`.
+      security:
+        - session: []
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [query, approve]
+              properties:
+                query: { type: string, description: "The `/oauth/authorize` query string, unchanged." }
+                approve: { type: boolean }
+      responses:
+        "200":
+          description: Where to go next.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  redirect_to: { type: string }
+        "400": { $ref: "#/components/responses/BadRequest" }
+        "403": { $ref: "#/components/responses/Forbidden" }
+
   /api/v1/mcp:
     post:
       tags: [integrations]
@@ -4426,21 +4481,27 @@ paths:
   /mcp:
     post:
       tags: [integrations]
-      summary: The MCP endpoint, with the token in the query string.
+      summary: The MCP endpoint at the address a person types into a connector.
       description: |
-        The same server as `/api/v1/mcp`, for a client that can only be given a
-        URL. Claude's custom-connector dialog asks for a name, an address and
-        OAuth client credentials — there is no field for a bearer token — so the
-        API path cannot be configured from it.
+        The same server as `/api/v1/mcp`. Two credentials are accepted: a bearer
+        token in `Authorization` — what a client holds after signing in with the
+        account through `/oauth/authorize` — or a token in `?key=`, for a client
+        that can only be given a URL.
 
-        The key is the only credential accepted here. A session cookie is
-        ignored: this route sits outside the CSRF check, and honouring a cookie
-        would make it a cross-site request that acts as whoever is signed in.
-      security: []
+        Without either, the 401 carries `WWW-Authenticate: Bearer
+        resource_metadata="…/.well-known/oauth-protected-resource/mcp"`, which is
+        how a client finds the sign-in.
+
+        A session cookie is ignored: this route sits outside the CSRF check, and
+        honouring a cookie would make it a cross-site request that acts as
+        whoever is signed in.
+      security:
+        - bearer: []
+        - {}
       parameters:
         - name: key
           in: query
-          required: true
+          required: false
           schema: { type: string, example: vrd_… }
           description: A personal API token. Treat the whole address as a password.
       requestBody:
@@ -4470,6 +4531,136 @@ paths:
         "202": { description: A notification. No body. }
         "401": { $ref: "#/components/responses/Unauthorized" }
 
+  /.well-known/oauth-protected-resource:
+    get:
+      tags: [integrations]
+      summary: Protected-resource metadata for the MCP endpoint (RFC 9728).
+      security: []
+      responses:
+        "200": { $ref: "#/components/responses/ProtectedResource" }
+
+  /.well-known/oauth-protected-resource/mcp:
+    get:
+      tags: [integrations]
+      summary: The same document, at the path RFC 9728 derives from `/mcp`.
+      security: []
+      responses:
+        "200": { $ref: "#/components/responses/ProtectedResource" }
+
+  /.well-known/oauth-authorization-server:
+    get:
+      tags: [integrations]
+      summary: Authorization-server metadata (RFC 8414).
+      description: |
+        The instance is its own authorization server, for MCP clients only.
+        Authorization code with S256 PKCE, public clients, no refresh tokens.
+      security: []
+      responses:
+        "200":
+          description: OK
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  issuer: { type: string }
+                  authorization_endpoint: { type: string }
+                  token_endpoint: { type: string }
+                  registration_endpoint: { type: string }
+                  code_challenge_methods_supported: { type: array, items: { type: string } }
+
+  /oauth/register:
+    post:
+      tags: [integrations]
+      summary: Dynamic client registration (RFC 7591).
+      description: |
+        Open to anybody, rate limited, public clients only. Redirect addresses
+        must be https, http on a loopback address (any port), or an app's own
+        scheme. Metadata the server does not use is ignored. A registration that
+        is never approved is removed after a day.
+      security: []
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [redirect_uris]
+              properties:
+                client_name: { type: string }
+                redirect_uris: { type: array, items: { type: string } }
+                token_endpoint_auth_method: { type: string, enum: [none] }
+      responses:
+        "201":
+          description: Registered.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  client_id: { type: string }
+                  client_name: { type: string }
+                  redirect_uris: { type: array, items: { type: string } }
+        "400": { $ref: "#/components/responses/OAuthError" }
+        "429": { description: Too many attempts. }
+
+  /oauth/authorize:
+    get:
+      tags: [integrations]
+      summary: Where a client sends the browser to sign in and approve.
+      description: |
+        Checks the request and redirects to the app's approval page, `/forbind`,
+        which signs the person in first if needed. An unknown client or an
+        unregistered redirect address is refused here with 400, and nothing is
+        sent anywhere; other problems are sent back to the client as `error=`.
+      security: []
+      parameters:
+        - { name: response_type, in: query, required: true, schema: { type: string, enum: [code] } }
+        - { name: client_id, in: query, required: true, schema: { type: string } }
+        - { name: redirect_uri, in: query, schema: { type: string } }
+        - { name: state, in: query, schema: { type: string } }
+        - { name: code_challenge, in: query, required: true, schema: { type: string } }
+        - { name: code_challenge_method, in: query, required: true, schema: { type: string, enum: [S256] } }
+      responses:
+        "302": { description: "To the approval page, or back to the client with an error." }
+        "400": { description: The client or its redirect address cannot be trusted. }
+
+  /oauth/token:
+    post:
+      tags: [integrations]
+      summary: Exchange an authorization code for a token.
+      description: |
+        `authorization_code` only. The code is good for one minute and one
+        attempt. The token is an ordinary personal API token, listed under
+        Settings → Tokens with the client's name; connecting the same client
+        again replaces it.
+      security: []
+      requestBody:
+        required: true
+        content:
+          application/x-www-form-urlencoded:
+            schema:
+              type: object
+              required: [grant_type, code, client_id, code_verifier]
+              properties:
+                grant_type: { type: string, enum: [authorization_code] }
+                code: { type: string }
+                client_id: { type: string }
+                redirect_uri: { type: string }
+                code_verifier: { type: string }
+      responses:
+        "200":
+          description: The token.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  access_token: { type: string, example: vrd_… }
+                  token_type: { type: string, const: Bearer }
+        "400": { $ref: "#/components/responses/OAuthError" }
+        "429": { description: Too many attempts. }
+
   /.well-known/caldav:
     get:
       tags: [integrations]
@@ -4504,6 +4695,24 @@ components:
         browser's own session is never accepted here.
 
   responses:
+    ProtectedResource:
+      description: OK
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              resource: { type: string, example: https://todo.example.dk/mcp }
+              authorization_servers: { type: array, items: { type: string } }
+    OAuthError:
+      description: The error shape of RFC 6749 §5.2.
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              error: { type: string, example: invalid_grant }
+              error_description: { type: string }
     BadRequest:
       description: The body could not be read.
       content:
@@ -5382,6 +5591,9 @@ components:
         created_at: { type: string, format: date-time }
         last_used_at: { type: string, format: date-time }
         expires_at: { type: string, format: date-time }
+        connected:
+          type: boolean
+          description: "True for a token an app received by signing in with the account, rather than one made by hand."
 
     Notification:
       type: object

internal/httpapi/edition_test.go

@@ -185,6 +185,10 @@ func TestNotesEditionServesOnlyItsOwnRoutes(t *testing.T) {
 		// er værktøjslisten bagved, der er kortere.
 		"POST /api/v1/mcp",
 		"POST /mcp",
+		// Og at forbinde med kontoen, som hører til MCP og ikke til opgaverne.
+		"GET /.well-known/oauth-authorization-server",
+		"POST /oauth/token",
+		"POST /api/v1/oauth/approve",
 	} {
 		if !notes[must] {
 			t.Errorf("the notes edition does not serve %s — that is a deletion, not a gate", must)

internal/httpapi/integrations_test.go

@@ -1172,17 +1172,16 @@ func TestMailAddressPrefersTheConfiguredSender(t *testing.T) {
 // namespace, and a client probing it is asking a yes-or-no question.
 //
 // Claude asks /.well-known/oauth-authorization-server before connecting to an
-// MCP server. It read the shell as "there is an authorization server here" and
-// then failed trying to register with it, reporting a broken sign-in service on
-// a server that has none and needs none.
+// MCP server. Before that was a real route it read the shell as "there is an
+// authorization server here" and failed trying to register with it. The OAuth
+// paths are answered by oauth_test.go now; everything else must still be a 404.
 func TestWellKnownDoesNotAnswerWithTheAppShell(t *testing.T) {
 	ts := newTestServer(t)
 	ts.bootstrap(t)
 
 	for _, path := range []string{
-		"/.well-known/oauth-authorization-server",
-		"/.well-known/oauth-protected-resource",
 		"/.well-known/openid-configuration",
+		"/.well-known/oauth-protected-resource/somewhere-else",
 		"/.well-known/anything-at-all",
 	} {
 		resp, err := ts.client.Get(ts.URL + path)

internal/httpapi/mcp_handlers.go

@@ -138,26 +138,34 @@ func (s *Server) handleMCP(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, response)
 }
 
-// handleMCPWithKey is the same endpoint for a client that can only be given a
-// URL: `POST /mcp?key=vrd_…`.
+// handleMCPWithKey is the same endpoint at the address a person types into a
+// connector dialog: `POST /mcp`. Two credentials are accepted here.
 //
-// Claude's custom-connector dialog asks for a name, an address and — under
-// advanced settings — an OAuth client id and secret. There is no field for a
-// bearer token, so /api/v1/mcp cannot be configured from it however correct the
-// address is. The calendar feed already carries its credential in the URL for
-// the same reason, and the request logger records the path without the query, so
-// the key does not end up in the log.
+// `Authorization: Bearer vrd_…` is what a client sends after signing in with the
+// account (oauth_handlers.go), and what anything holding a token by hand can
+// send as well.
 //
-// The key is the *only* thing accepted here. Reading a session cookie instead
-// would make this a state-changing POST outside the CSRF check — which is to say
-// a cross-site request that acts as whoever is signed in.
+// `?key=vrd_…` is for a client that can only be given a URL. Claude's
+// custom-connector dialog has no field for a header, so before the sign-in
+// existed this was the only way to configure it, and addresses made that way
+// still work. The calendar feed carries its credential in the URL for the same
+// reason, and the request logger records the path without the query, so the key
+// does not end up in the log.
+//
+// A session cookie is *never* accepted here. That would make this a
+// state-changing POST outside the CSRF check — a cross-site request that acts as
+// whoever is signed in. A bearer header is safe where a cookie is not: a browser
+// will not attach one to a cross-site request by itself.
 func (s *Server) handleMCPWithKey(w http.ResponseWriter, r *http.Request) {
 	key := r.URL.Query().Get("key")
+	if h := r.Header.Get("Authorization"); key == "" && strings.HasPrefix(h, "Bearer ") {
+		key = strings.TrimSpace(strings.TrimPrefix(h, "Bearer "))
+	}
 	if key == "" || !auth.IsAPIToken(key) {
 		// 401 rather than 404: unlike a task, the existence of this endpoint is
-		// not a secret — it is written in the documentation.
-		writeError(w, http.StatusUnauthorized, CodeUnauthorized,
-			"add ?key=<api token> to the URL")
+		// not a secret — it is written in the documentation. And the header is
+		// what starts the sign-in: it tells the client where to read how.
+		s.mcpUnauthorized(w, "sign in, or add ?key=<api token> to the URL")
 		return
 	}
 
@@ -167,13 +175,22 @@ func (s *Server) handleMCPWithKey(w http.ResponseWriter, r *http.Request) {
 			s.internal(w, r, "mcp key", err)
 			return
 		}
-		writeError(w, http.StatusUnauthorized, CodeUnauthorized, "that key is not valid")
+		// Also the answer to a token revoked under Settings, which is why the
+		// header is here too: the client then asks the person to sign in again.
+		s.mcpUnauthorized(w, "that key is not valid")
 		return
 	}
 
 	s.handleMCP(w, r.WithContext(withUser(r.Context(), user)))
 }
 
+// mcpUnauthorized is the 401 that points a client at the sign-in (RFC 9728 §5.1).
+func (s *Server) mcpUnauthorized(w http.ResponseWriter, message string) {
+	w.Header().Set("WWW-Authenticate",
+		`Bearer resource_metadata="`+s.protectedResourceMetadataURL()+`"`)
+	writeError(w, http.StatusUnauthorized, CodeUnauthorized, message)
+}
+
 // --- tool implementations ------------------------------------------------------------
 
 func (s *Server) mcpListProjects(ctx context.Context, userID string, args json.RawMessage) (any, error) {

internal/httpapi/oauth_handlers.go

@@ -0,0 +1,558 @@
+package httpapi
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+	"unicode"
+
+	"github.com/kristianwind/verdande/internal/store"
+)
+
+// Signing in to MCP with the account, rather than with a token pasted into a URL.
+//
+// Claude's connector dialog tries OAuth before anything else: it asks
+// /.well-known for an authorization server, registers itself, sends the person
+// to sign in and approve, and comes back with a code. Until this existed the
+// answer was a 404, and the only way in was to make a token under Settings and
+// paste it into the address — a secret copied between two programs, which is the
+// step people stopped at.
+//
+// The shape is the smallest one the MCP authorization spec asks for:
+//
+//   - discovery: protected-resource metadata (RFC 9728) pointing at this instance
+//     as its own authorization server (RFC 8414);
+//   - dynamic client registration (RFC 7591), public clients only — a program
+//     running somewhere else cannot keep a secret, so PKCE is the proof instead;
+//   - the authorization-code grant with S256 PKCE, and nothing else.
+//
+// What an approval hands out is an ordinary personal API token. That is the
+// whole permission model: a token is a person, it is listed under Settings →
+// Tokens next to the hand-made ones, and revoking it there disconnects the
+// client. No refresh token and no expiry, because there is nothing for one to
+// protect that the token page does not already — a client that is cut off is
+// answered 401 and asks the person to sign in again.
+
+const oauthCodeTTL = time.Minute
+
+// oauthGrant is what an authorization code stands for until it is exchanged.
+type oauthGrant struct {
+	userID      string
+	clientID    string
+	redirectURI string
+	challenge   string
+	scope       string
+	expires     time.Time
+}
+
+// oauthCodes are held in memory, like the socket tickets: good for a minute and
+// once. A restart in that minute costs one more click, which is cheaper than a
+// table of short-lived secrets.
+type oauthCodes struct {
+	mu sync.Mutex
+	m  map[string]oauthGrant
+}
+
+func newOAuthCodes() *oauthCodes { return &oauthCodes{m: map[string]oauthGrant{}} }
+
+func (c *oauthCodes) issue(g oauthGrant) (string, error) {
+	raw := make([]byte, 32)
+	if _, err := rand.Read(raw); err != nil {
+		return "", err
+	}
+	code := hex.EncodeToString(raw)
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	now := time.Now()
+	for k, v := range c.m {
+		if now.After(v.expires) {
+			delete(c.m, k)
+		}
+	}
+	g.expires = now.Add(oauthCodeTTL)
+	c.m[code] = g
+	return code, nil
+}
+
+// redeem spends a code. Deleted before it is checked, so a code presented twice
+// fails the second time whatever the first one did — a replayed code is the
+// thing PKCE and single use are both there to stop.
+func (c *oauthCodes) redeem(code string) (oauthGrant, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	g, ok := c.m[code]
+	delete(c.m, code)
+	if !ok || time.Now().After(g.expires) {
+		return oauthGrant{}, false
+	}
+	return g, true
+}
+
+// --- discovery -----------------------------------------------------------------------
+
+// mcpResource is the address the protected resource is known by: the URL a
+// person types into the connector dialog.
+func (s *Server) mcpResource() string { return s.cfg.BaseURL + "/mcp" }
+
+func (s *Server) protectedResourceMetadataURL() string {
+	return s.cfg.BaseURL + "/.well-known/oauth-protected-resource/mcp"
+}
+
+func (s *Server) handleProtectedResourceMetadata(w http.ResponseWriter, r *http.Request) {
+	openCORS(w)
+	writeJSON(w, http.StatusOK, map[string]any{
+		"resource":                 s.mcpResource(),
+		"authorization_servers":    []string{s.cfg.BaseURL},
+		"bearer_methods_supported": []string{"header"},
+		"resource_name":            s.cfg.ProductSlug(),
+	})
+}
+
+func (s *Server) handleAuthorizationServerMetadata(w http.ResponseWriter, r *http.Request) {
+	openCORS(w)
+	base := s.cfg.BaseURL
+	writeJSON(w, http.StatusOK, map[string]any{
+		"issuer":                                base,
+		"authorization_endpoint":                base + "/oauth/authorize",
+		"token_endpoint":                        base + "/oauth/token",
+		"registration_endpoint":                 base + "/oauth/register",
+		"response_types_supported":              []string{"code"},
+		"grant_types_supported":                 []string{"authorization_code"},
+		"code_challenge_methods_supported":      []string{"S256"},
+		"token_endpoint_auth_methods_supported": []string{"none"},
+	})
+}
+
+// openCORS lets a browser-based client read these answers. Safe for exactly the
+// routes it is on: none of them reads a cookie, so a cross-site caller learns
+// nothing and can do nothing it could not do with curl.
+func openCORS(w http.ResponseWriter) {
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
+	w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
+}
+
+func handleOpenPreflight(w http.ResponseWriter, r *http.Request) {
+	openCORS(w)
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// oauthError is the error shape RFC 6749 §5.2 prescribes for the token and
+// registration endpoints — a client library parses `error`, not our `code`.
+func oauthError(w http.ResponseWriter, status int, code, description string) {
+	w.Header().Set("Cache-Control", "no-store")
+	writeJSON(w, status, map[string]string{"error": code, "error_description": description})
+}
+
+// --- registration --------------------------------------------------------------------
+
+type registerRequest struct {
+	ClientName              string   `json:"client_name"`
+	RedirectURIs            []string `json:"redirect_uris"`
+	TokenEndpointAuthMethod string   `json:"token_endpoint_auth_method"`
+}
+
+func (s *Server) handleOAuthRegister(w http.ResponseWriter, r *http.Request) {
+	openCORS(w)
+
+	// Not decodeJSON: a registration request carries whatever metadata the
+	// client library fills in — logo_uri, grant_types, scope, contacts — and
+	// RFC 7591 says a server ignores what it does not use. Refusing unknown
+	// fields here would refuse every real client.
+	var req registerRequest
+	if err := decodeLenient(r, &req); err != nil {
+		oauthError(w, http.StatusBadRequest, "invalid_client_metadata", "the body is not JSON")
+		return
+	}
+
+	if len(req.RedirectURIs) == 0 || len(req.RedirectURIs) > 10 {
+		oauthError(w, http.StatusBadRequest, "invalid_redirect_uri",
+			"between one and ten redirect_uris are required")
+		return
+	}
+	for _, u := range req.RedirectURIs {
+		if !validRedirectURI(u) {
+			oauthError(w, http.StatusBadRequest, "invalid_redirect_uri",
+				"redirect_uris must be https, http on a loopback address, or an app's own scheme: "+u)
+			return
+		}
+	}
+	if m := req.TokenEndpointAuthMethod; m != "" && m != "none" {
+		// Said rather than silently downgraded: a client that believes it holds a
+		// secret would send one and wonder why it was ignored.
+		oauthError(w, http.StatusBadRequest, "invalid_client_metadata",
+			"only public clients are supported; use token_endpoint_auth_method \"none\" with PKCE")
+		return
+	}
+
+	name := cleanClientName(req.ClientName)
+	client, err := s.db.CreateOAuthClient(r.Context(), name, req.RedirectURIs)
+	if err != nil {
+		s.internal(w, r, "register oauth client", err)
+		return
+	}
+
+	w.Header().Set("Cache-Control", "no-store")
+	writeJSON(w, http.StatusCreated, map[string]any{
+		"client_id":                  client.ID,
+		"client_id_issued_at":        client.CreatedAt.Unix(),
+		"client_name":                client.Name,
+		"redirect_uris":              client.RedirectURIs,
+		"grant_types":                []string{"authorization_code"},
+		"response_types":             []string{"code"},
+		"token_endpoint_auth_method": "none",
+	})
+}
+
+// cleanClientName makes the self-declared name fit to show. It is shown on the
+// approval screen and on the tokens page, so it is trimmed, stripped of control
+// characters and capped — and it is never trusted to say who the client is: the
+// approval screen also shows where the code will be sent, which a client cannot
+// choose to misstate.
+func cleanClientName(name string) string {
+	name = strings.Map(func(r rune) rune {
+		if unicode.IsControl(r) {
+			return -1
+		}
+		return r
+	}, strings.TrimSpace(name))
+	if runes := []rune(name); len(runes) > 60 {
+		name = strings.TrimSpace(string(runes[:60]))
+	}
+	if name == "" {
+		name = "MCP-klient"
+	}
+	return name
+}
+
+// validRedirectURI is the rule for where a code may be sent.
+//
+// https anywhere; plain http only to this machine's loopback (RFC 8252 §7.3,
+// where a desktop client listens on a port it picks at run time); and an app's
+// own scheme (§7.1), which is how Cursor and its like receive one. The schemes a
+// browser would *run* rather than navigate to are refused by name — the approval
+// page hands the address to `location`, and `javascript:` there is script
+// running on this origin.
+func validRedirectURI(raw string) bool {
+	if len(raw) > 2000 {
+		return false
+	}
+	u, err := url.Parse(raw)
+	if err != nil || u.Fragment != "" || u.Scheme == "" {
+		return false
+	}
+	switch scheme := strings.ToLower(u.Scheme); scheme {
+	case "https":
+		return u.Host != ""
+	case "http":
+		return isLoopback(u.Hostname())
+	case "javascript", "data", "file", "vbscript", "blob", "about", "ws", "wss", "ftp":
+		return false
+	default:
+		// The scheme's own syntax, RFC 3986 §3.1. url.Parse is lenient about it.
+		for i, r := range scheme {
+			if !(r >= 'a' && r <= 'z' || i > 0 && (r >= '0' && r <= '9' || r == '+' || r == '-' || r == '.')) {
+				return false
+			}
+		}
+		return true
+	}
+}
+
+func isLoopback(host string) bool {
+	if host == "localhost" {
+		return true
+	}
+	ip := net.ParseIP(host)
+	return ip != nil && ip.IsLoopback()
+}
+
+// redirectAllowed reports whether got is one of the client's registered
+// addresses. Exact, except that a loopback address may differ in its port: a
+// desktop client registers once and listens wherever the OS lets it next time.
+func redirectAllowed(registered []string, got string) bool {
+	for _, want := range registered {
+		if want == got {
+			return true
+		}
+	}
+	g, err := url.Parse(got)
+	if err != nil || g.Scheme != "http" || !isLoopback(g.Hostname()) {
+		return false
+	}
+	for _, want := range registered {
+		w, err := url.Parse(want)
+		if err != nil || w.Scheme != "http" || !isLoopback(w.Hostname()) {
+			continue
+		}
+		if w.Hostname() == g.Hostname() && w.Path == g.Path && w.RawQuery == g.RawQuery {
+			return true
+		}
+	}
+	return false
+}
+
+// --- authorization -------------------------------------------------------------------
+
+// authorizeRequest is a checked /oauth/authorize query.
+type authorizeRequest struct {
+	client      *store.OAuthClient
+	redirectURI string
+	state       string
+	challenge   string
+	scope       string
+}
+
+// errBadClient means the client or its redirect address could not be trusted,
+// so the answer must NOT be sent to that address (RFC 6749 §4.1.2.1) — it is
+// shown to the person instead. Every other problem goes back to the client.
+var errBadClient = errors.New("bad client")
+
+// checkAuthorize validates a query. It runs twice — when the browser arrives,
+// and again when the person presses approve — because the approval page is a
+// page in the app, and what it posts back is whatever is in its address bar.
+func (s *Server) checkAuthorize(r *http.Request, q url.Values) (*authorizeRequest, string, error) {
+	client, err := s.db.OAuthClient(r.Context(), q.Get("client_id"))
+	if err != nil {
+		if errors.Is(err, store.ErrNotFound) {
+			return nil, "this app is not registered here — remove the connection and add it again", errBadClient
+		}
+		return nil, "", err
+	}
+	redirect := q.Get("redirect_uri")
+	if redirect == "" && len(client.RedirectURIs) == 1 {
+		redirect = client.RedirectURIs[0]
+	}
+	if !redirectAllowed(client.RedirectURIs, redirect) {
+		return nil, "the app asked to be answered at an address it did not register", errBadClient
+	}
+
+	req := &authorizeRequest{
+		client: client, redirectURI: redirect,
+		state: q.Get("state"), challenge: q.Get("code_challenge"), scope: q.Get("scope"),
+	}
+	switch {
+	case q.Get("response_type") != "code":
+		return req, "unsupported_response_type", nil
+	case req.challenge == "" || q.Get("code_challenge_method") != "S256":
+		// OAuth 2.1 makes PKCE mandatory, and plain PKCE protects nothing that
+		// S256 does not, so it is S256 or no code.
+		return req, "invalid_request", nil
+	}
+	return req, "", nil
+}
+
+// redirectWith builds the address the browser is sent back to. Callers include
+// `iss` (RFC 9207): it says who answered, so a client talking to several servers
+// cannot be handed one server's code by another.
+func (a *authorizeRequest) redirectWith(params url.Values) string {
+	if a.state != "" {
+		params.Set("state", a.state)
+	}
+	sep := "?"
+	if strings.Contains(a.redirectURI, "?") {
+		sep = "&"
+	}
+	return a.redirectURI + sep + params.Encode()
+}
+
+// handleOAuthAuthorize is where the client sends the browser. It checks the
+// request and hands over to the app's approval page, which signs the person in
+// first if it needs to — the same sign-in screen, passkeys and second factor
+// included, rather than a second, lesser one written for OAuth.
+func (s *Server) handleOAuthAuthorize(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	req, problem, err := s.checkAuthorize(r, q)
+	if errors.Is(err, errBadClient) {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte(s.cfg.ProductSlug() + ": " + problem + ".\n"))
+		return
+	}
+	if err != nil {
+		s.internal(w, r, "oauth authorize", err)
+		return
+	}
+	if problem != "" {
+		http.Redirect(w, r, req.redirectWith(url.Values{
+			"error": {problem}, "iss": {s.cfg.BaseURL},
+		}), http.StatusFound)
+		return
+	}
+	http.Redirect(w, r, "/forbind?"+r.URL.RawQuery, http.StatusFound)
+}
+
+// handleOAuthRequest tells the approval page what it is approving.
+func (s *Server) handleOAuthRequest(w http.ResponseWriter, r *http.Request) {
+	req, problem, err := s.checkAuthorize(r, r.URL.Query())
+	if err != nil && !errors.Is(err, errBadClient) {
+		s.internal(w, r, "oauth request", err)
+		return
+	}
+	if err == nil && problem != "" {
+		problem = "the app's request is not valid (" + problem + ")"
+	}
+	if problem != "" {
+		writeError(w, http.StatusBadRequest, CodeBadRequest, problem)
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{
+		"client_name": req.client.Name,
+		// Where the code goes, which is the part a client cannot lie about. Any
+		// program can register itself as "Claude"; only Claude is answered at
+		// claude.ai.
+		"redirect_to": redirectLabel(req.redirectURI),
+	})
+}
+
+func redirectLabel(raw string) string {
+	u, err := url.Parse(raw)
+	if err != nil {
+		return raw
+	}
+	if u.Host != "" {
+		return u.Hostname()
+	}
+	return u.Scheme + ":"
+}
+
+type approveRequest struct {
+	// Query is the approval page's own query string, exactly as the client sent
+	// it. Posted whole rather than as fields, so this and handleOAuthAuthorize
+	// read one thing with one function and cannot drift apart.
+	Query   string `json:"query"`
+	Approve bool   `json:"approve"`
+}
+
+// handleOAuthApprove is the person's answer. Behind requireSession: an approval
+// mints a token, and a token must not be able to mint another.
+func (s *Server) handleOAuthApprove(w http.ResponseWriter, r *http.Request) {
+	var body approveRequest
+	if err := decodeJSON(w, r, &body); err != nil {
+		return
+	}
+	q, err := url.ParseQuery(strings.TrimPrefix(body.Query, "?"))
+	if err != nil {
+		writeError(w, http.StatusBadRequest, CodeBadRequest, "the request could not be read")
+		return
+	}
+	req, problem, err := s.checkAuthorize(r, q)
+	if err != nil && !errors.Is(err, errBadClient) {
+		s.internal(w, r, "oauth approve", err)
+		return
+	}
+	if err == nil && problem != "" {
+		problem = "the app's request is not valid (" + problem + ")"
+	}
+	if problem != "" {
+		writeError(w, http.StatusBadRequest, CodeBadRequest, problem)
+		return
+	}
+
+	if !body.Approve {
+		writeJSON(w, http.StatusOK, map[string]string{"redirect_to": req.redirectWith(url.Values{
+			"error": {"access_denied"}, "iss": {s.cfg.BaseURL},
+		})})
+		return
+	}
+
+	code, err := s.oauthCodes.issue(oauthGrant{
+		userID: userFrom(r.Context()).ID, clientID: req.client.ID,
+		redirectURI: req.redirectURI, challenge: req.challenge, scope: req.scope,
+	})
+	if err != nil {
+		s.internal(w, r, "oauth code", err)
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]string{"redirect_to": req.redirectWith(url.Values{
+		"code": {code}, "iss": {s.cfg.BaseURL},
+	})})
+}
+
+// --- token ---------------------------------------------------------------------------
+
+func (s *Server) handleOAuthToken(w http.ResponseWriter, r *http.Request) {
+	openCORS(w)
+	r.Body = http.MaxBytesReader(w, r.Body, 16<<10)
+	if err := r.ParseForm(); err != nil {
+		oauthError(w, http.StatusBadRequest, "invalid_request", "the body must be form-encoded")
+		return
+	}
+	if gt := r.PostForm.Get("grant_type"); gt != "authorization_code" {
+		oauthError(w, http.StatusBadRequest, "unsupported_grant_type",
+			"only authorization_code is supported")
+		return
+	}
+
+	clientID := r.PostForm.Get("client_id")
+	if id, _, ok := r.BasicAuth(); ok && clientID == "" {
+		clientID = id
+	}
+
+	grant, ok := s.oauthCodes.redeem(r.PostForm.Get("code"))
+	if !ok {
+		oauthError(w, http.StatusBadRequest, "invalid_grant", "the code is unknown, used or expired")
+		return
+	}
+	// Each of these is a code presented by somebody other than the one it was
+	// issued to, or for somewhere else. The code is already spent either way.
+	if clientID != grant.clientID {
+		oauthError(w, http.StatusBadRequest, "invalid_grant", "the code was issued to another client")
+		return
+	}
+	if ru := r.PostForm.Get("redirect_uri"); ru != "" && ru != grant.redirectURI {
+		oauthError(w, http.StatusBadRequest, "invalid_grant", "redirect_uri does not match the authorization")
+		return
+	}
+	if !pkceMatches(r.PostForm.Get("code_verifier"), grant.challenge) {
+		oauthError(w, http.StatusBadRequest, "invalid_grant", "code_verifier does not match")
+		return
+	}
+
+	client, err := s.db.OAuthClient(r.Context(), grant.clientID)
+	if err != nil {
+		oauthError(w, http.StatusBadRequest, "invalid_client", "the client is no longer registered")
+		return
+	}
+	token, err := s.db.CreateOAuthToken(r.Context(), grant.userID, client)
+	if err != nil {
+		s.internal(w, r, "oauth token", err)
+		return
+	}
+
+	w.Header().Set("Cache-Control", "no-store")
+	out := map[string]string{"access_token": token, "token_type": "Bearer"}
+	if grant.scope != "" {
+		out["scope"] = grant.scope
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
+// pkceMatches is RFC 7636 §4.6 for S256: the challenge is the unpadded base64url
+// SHA-256 of the verifier.
+func pkceMatches(verifier, challenge string) bool {
+	if len(verifier) < 43 || len(verifier) > 128 {
+		return false
+	}
+	sum := sha256.Sum256([]byte(verifier))
+	want := base64.RawURLEncoding.EncodeToString(sum[:])
+	return subtle.ConstantTimeCompare([]byte(want), []byte(challenge)) == 1
+}
+
+// decodeLenient reads a JSON body that may carry fields this server does not
+// use. Only for the registration endpoint — see the comment there.
+func decodeLenient(r *http.Request, dst any) error {
+	return json.NewDecoder(io.LimitReader(r.Body, 64<<10)).Decode(dst)
+}

internal/httpapi/oauth_test.go

@@ -0,0 +1,398 @@
+package httpapi
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+)
+
+// Signing in to MCP with the account: the whole dance Claude performs, from the
+// first 401 to a tool call made with the token it was handed.
+
+const claudeCallback = "https://claude.ai/api/mcp/auth_callback"
+
+// A verifier of the minimum legal length, and its S256 challenge.
+var (
+	testVerifier  = strings.Repeat("v", 43)
+	testChallenge = func() string {
+		sum := sha256.Sum256([]byte(testVerifier))
+		return base64.RawURLEncoding.EncodeToString(sum[:])
+	}()
+)
+
+func postJSON(t *testing.T, target, body string) (*http.Response, map[string]any) {
+	t.Helper()
+	resp, err := http.Post(target, "application/json", strings.NewReader(body))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	var decoded map[string]any
+	_ = json.NewDecoder(resp.Body).Decode(&decoded)
+	return resp, decoded
+}
+
+// registerClient registers the way Claude does, extra metadata included.
+func registerClient(t *testing.T, ts *testServer, redirect string) string {
+	t.Helper()
+	resp, body := postJSON(t, ts.URL+"/oauth/register", `{
+		"client_name": "Claude",
+		"redirect_uris": ["`+redirect+`"],
+		"grant_types": ["authorization_code", "refresh_token"],
+		"response_types": ["code"],
+		"token_endpoint_auth_method": "none",
+		"scope": "claudeai"
+	}`)
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf("register: status %d, %v", resp.StatusCode, body)
+	}
+	id, _ := body["client_id"].(string)
+	if id == "" {
+		t.Fatalf("register: no client_id in %v", body)
+	}
+	return id
+}
+
+func authorizeQuery(clientID, redirect string) string {
+	return url.Values{
+		"response_type":         {"code"},
+		"client_id":             {clientID},
+		"redirect_uri":          {redirect},
+		"state":                 {"st4te"},
+		"code_challenge":        {testChallenge},
+		"code_challenge_method": {"S256"},
+		"resource":              {"http://localhost/mcp"},
+	}.Encode()
+}
+
+// approve is the approval page pressing "Tillad", as the signed-in ts.client.
+// It returns the code from the address the browser is sent back to.
+func approve(t *testing.T, ts *testServer, query string) string {
+	t.Helper()
+	resp, body := ts.do(t, "POST", "/api/v1/oauth/approve", map[string]any{
+		"query": "?" + query, "approve": true,
+	})
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("approve: status %d, %v", resp.StatusCode, body)
+	}
+	back, err := url.Parse(body["redirect_to"].(string))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := back.Query().Get("state"); got != "st4te" {
+		t.Errorf("state = %q, want it handed back unchanged", got)
+	}
+	return back.Query().Get("code")
+}
+
+func exchange(t *testing.T, ts *testServer, form url.Values) (*http.Response, map[string]any) {
+	t.Helper()
+	resp, err := http.PostForm(ts.URL+"/oauth/token", form)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	var decoded map[string]any
+	_ = json.NewDecoder(resp.Body).Decode(&decoded)
+	return resp, decoded
+}
+
+func codeForm(clientID, code string) url.Values {
+	return url.Values{
+		"grant_type": {"authorization_code"}, "code": {code}, "client_id": {clientID},
+		"redirect_uri": {claudeCallback}, "code_verifier": {testVerifier},
+	}
+}
+
+func mcpInitialize(t *testing.T, ts *testServer, bearer string) *http.Response {
+	t.Helper()
+	req, _ := http.NewRequest("POST", ts.URL+"/mcp",
+		strings.NewReader(`{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}`))
+	req.Header.Set("Content-Type", "application/json")
+	if bearer != "" {
+		req.Header.Set("Authorization", "Bearer "+bearer)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resp.Body.Close()
+	return resp
+}
+
+func TestMCPSignInWithTheAccount(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+
+	// 1. The connector's first request has no credential, and the answer says
+	//    where to read how to get one.
+	resp := mcpInitialize(t, ts, "")
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("unauthenticated /mcp: status %d", resp.StatusCode)
+	}
+	challenge := resp.Header.Get("WWW-Authenticate")
+	want := `resource_metadata="http://localhost/.well-known/oauth-protected-resource/mcp"`
+	if !strings.Contains(challenge, want) {
+		t.Fatalf("WWW-Authenticate = %q, want it to contain %s", challenge, want)
+	}
+
+	// 2. Discovery, both documents.
+	var prm, asm map[string]any
+	for path, into := range map[string]*map[string]any{
+		"/.well-known/oauth-protected-resource/mcp": &prm,
+		"/.well-known/oauth-authorization-server":   &asm,
+	} {
+		r, err := http.Get(ts.URL + path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		json.NewDecoder(r.Body).Decode(into)
+		r.Body.Close()
+		if r.StatusCode != http.StatusOK {
+			t.Fatalf("%s: status %d", path, r.StatusCode)
+		}
+	}
+	if prm["resource"] != "http://localhost/mcp" {
+		t.Errorf("resource = %v, want the address a person types in", prm["resource"])
+	}
+	if asm["issuer"] != "http://localhost" || asm["registration_endpoint"] != "http://localhost/oauth/register" {
+		t.Errorf("authorization server metadata = %v", asm)
+	}
+
+	// 3. Registration, 4. the browser's visit, 5. approval, 6. the exchange.
+	clientID := registerClient(t, ts, claudeCallback)
+	query := authorizeQuery(clientID, claudeCallback)
+
+	noFollow := &http.Client{CheckRedirect: func(*http.Request, []*http.Request) error {
+		return http.ErrUseLastResponse
+	}}
+	r, err := noFollow.Get(ts.URL + "/oauth/authorize?" + query)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Body.Close()
+	if loc := r.Header.Get("Location"); r.StatusCode != http.StatusFound || !strings.HasPrefix(loc, "/forbind?") {
+		t.Fatalf("authorize: status %d, Location %q — want the approval page", r.StatusCode, loc)
+	}
+
+	// The approval page's question: what is this, and where does it go.
+	info, body := ts.do(t, "GET", "/api/v1/oauth/request?"+query, nil)
+	if info.StatusCode != http.StatusOK || body["client_name"] != "Claude" || body["redirect_to"] != "claude.ai" {
+		t.Fatalf("request info: status %d, %v", info.StatusCode, body)
+	}
+
+	code := approve(t, ts, query)
+	tokResp, tok := exchange(t, ts, codeForm(clientID, code))
+	if tokResp.StatusCode != http.StatusOK {
+		t.Fatalf("token: status %d, %v", tokResp.StatusCode, tok)
+	}
+	access, _ := tok["access_token"].(string)
+	if tok["token_type"] != "Bearer" || !strings.HasPrefix(access, "vrd_") {
+		t.Fatalf("token response = %v", tok)
+	}
+	if cc := tokResp.Header.Get("Cache-Control"); cc != "no-store" {
+		t.Errorf("Cache-Control = %q on a response carrying a token", cc)
+	}
+
+	// 7. The token works where the person typed the address.
+	if resp := mcpInitialize(t, ts, access); resp.StatusCode != http.StatusOK {
+		t.Fatalf("/mcp with the token: status %d", resp.StatusCode)
+	}
+
+	// 8. And it is on the tokens page, under the client's name, marked as such.
+	_, list := ts.do(t, "GET", "/api/v1/tokens", nil)
+	tokens, _ := list["tokens"].([]any)
+	if len(tokens) != 1 {
+		t.Fatalf("tokens page lists %d, want 1: %v", len(tokens), list)
+	}
+	entry := tokens[0].(map[string]any)
+	if entry["name"] != "Claude" || entry["connected"] != true {
+		t.Errorf("token entry = %v", entry)
+	}
+
+	// 9. Revoked there, the client is told to sign in again.
+	if resp, _ := ts.do(t, "DELETE", "/api/v1/tokens/"+entry["id"].(string), nil); resp.StatusCode != http.StatusNoContent {
+		t.Fatalf("revoke: status %d", resp.StatusCode)
+	}
+	resp = mcpInitialize(t, ts, access)
+	if resp.StatusCode != http.StatusUnauthorized || resp.Header.Get("WWW-Authenticate") == "" {
+		t.Errorf("revoked token: status %d, WWW-Authenticate %q", resp.StatusCode, resp.Header.Get("WWW-Authenticate"))
+	}
+}
+
+// A code is good once. A second exchange — a replay, or a code that leaked — gets
+// nothing, and neither does a wrong verifier, the wrong client or the wrong
+// redirect: each is somebody other than the one the code was issued to.
+func TestOAuthCodeIsBoundAndSingleUse(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+	clientID := registerClient(t, ts, claudeCallback)
+	other := registerClient(t, ts, claudeCallback)
+	query := authorizeQuery(clientID, claudeCallback)
+
+	cases := map[string]func(url.Values){
+		"wrong verifier": func(f url.Values) { f.Set("code_verifier", strings.Repeat("w", 43)) },
+		"no verifier":    func(f url.Values) { f.Del("code_verifier") },
+		"other client":   func(f url.Values) { f.Set("client_id", other) },
+		"other redirect": func(f url.Values) { f.Set("redirect_uri", "https://claude.ai/elsewhere") },
+	}
+	for name, spoil := range cases {
+		code := approve(t, ts, query)
+		form := codeForm(clientID, code)
+		spoil(form)
+		if resp, body := exchange(t, ts, form); resp.StatusCode != http.StatusBadRequest || body["error"] != "invalid_grant" {
+			t.Errorf("%s: status %d, %v — want invalid_grant", name, resp.StatusCode, body)
+		}
+		// Spent by the failed attempt, so the rightful owner cannot use it either.
+		if resp, _ := exchange(t, ts, codeForm(clientID, code)); resp.StatusCode != http.StatusBadRequest {
+			t.Errorf("%s: the code survived a failed exchange", name)
+		}
+	}
+
+	code := approve(t, ts, query)
+	if resp, _ := exchange(t, ts, codeForm(clientID, code)); resp.StatusCode != http.StatusOK {
+		t.Fatalf("first exchange: status %d", resp.StatusCode)
+	}
+	if resp, body := exchange(t, ts, codeForm(clientID, code)); resp.StatusCode != http.StatusBadRequest {
+		t.Errorf("replayed code: status %d, %v", resp.StatusCode, body)
+	}
+}
+
+// Where a code may be sent is the whole security of the approval: a client
+// registers its addresses, and a request for any other is refused without
+// sending anything anywhere.
+func TestOAuthRedirectRules(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+
+	for _, bad := range []string{
+		"javascript:alert(1)",
+		"data:text/html,hi",
+		"http://evil.example/cb", // plain http off this machine
+		"https://claude.ai/cb#frag",
+		"not a uri",
+	} {
+		resp, body := postJSON(t, ts.URL+"/oauth/register",
+			`{"client_name":"x","redirect_uris":[`+jsonString(bad)+`]}`)
+		if resp.StatusCode != http.StatusBadRequest || body["error"] != "invalid_redirect_uri" {
+			t.Errorf("registering %q: status %d, %v", bad, resp.StatusCode, body)
+		}
+	}
+
+	clientID := registerClient(t, ts, claudeCallback)
+	noFollow := &http.Client{CheckRedirect: func(*http.Request, []*http.Request) error {
+		return http.ErrUseLastResponse
+	}}
+	r, err := noFollow.Get(ts.URL + "/oauth/authorize?" + authorizeQuery(clientID, "https://evil.example/cb"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Body.Close()
+	if r.StatusCode != http.StatusBadRequest || r.Header.Get("Location") != "" {
+		t.Errorf("unregistered redirect: status %d, Location %q — want a refusal shown here",
+			r.StatusCode, r.Header.Get("Location"))
+	}
+	resp, _ := ts.do(t, "POST", "/api/v1/oauth/approve", map[string]any{
+		"query": authorizeQuery(clientID, "https://evil.example/cb"), "approve": true,
+	})
+	if resp.StatusCode != http.StatusBadRequest {
+		t.Errorf("approving an unregistered redirect: status %d", resp.StatusCode)
+	}
+
+	// A desktop client listens on whatever port it is given that day.
+	loopback := registerClient(t, ts, "http://127.0.0.1/callback")
+	r, err = noFollow.Get(ts.URL + "/oauth/authorize?" + authorizeQuery(loopback, "http://127.0.0.1:53682/callback"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Body.Close()
+	if r.StatusCode != http.StatusFound || !strings.HasPrefix(r.Header.Get("Location"), "/forbind?") {
+		t.Errorf("loopback with a port: status %d, Location %q", r.StatusCode, r.Header.Get("Location"))
+	}
+
+	// No PKCE is answered to the client — its address is trusted by now.
+	q, _ := url.ParseQuery(authorizeQuery(clientID, claudeCallback))
+	q.Del("code_challenge")
+	r, err = noFollow.Get(ts.URL + "/oauth/authorize?" + q.Encode())
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Body.Close()
+	if loc := r.Header.Get("Location"); !strings.HasPrefix(loc, claudeCallback+"?") || !strings.Contains(loc, "error=invalid_request") {
+		t.Errorf("no PKCE: Location %q", loc)
+	}
+}
+
+// An approval mints a token, so a token must not be able to approve: otherwise
+// one leaked token is a machine for making more that survive its revocation.
+func TestOAuthApprovalNeedsASession(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+	var userID string
+	if err := ts.db.QueryRowContext(t.Context(), `SELECT id FROM users LIMIT 1`).Scan(&userID); err != nil {
+		t.Fatal(err)
+	}
+	key := ts.apiToken(t, userID)
+	clientID := registerClient(t, ts, claudeCallback)
+
+	req, _ := http.NewRequest("POST", ts.URL+"/api/v1/oauth/approve",
+		strings.NewReader(`{"query":"`+authorizeQuery(clientID, claudeCallback)+`","approve":true}`))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+key)
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	io.Copy(io.Discard, resp.Body)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusForbidden {
+		t.Errorf("approval with an API token: status %d, want 403", resp.StatusCode)
+	}
+}
+
+// "Afvis" sends the client away with access_denied and no code.
+func TestOAuthDenial(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+	clientID := registerClient(t, ts, claudeCallback)
+
+	_, body := ts.do(t, "POST", "/api/v1/oauth/approve", map[string]any{
+		"query": authorizeQuery(clientID, claudeCallback), "approve": false,
+	})
+	back, _ := url.Parse(body["redirect_to"].(string))
+	if back.Query().Get("error") != "access_denied" || back.Query().Get("code") != "" {
+		t.Errorf("denial redirect = %v", body["redirect_to"])
+	}
+}
+
+// Connecting the same client again replaces its token rather than adding one.
+func TestOAuthReconnectReplacesTheToken(t *testing.T) {
+	ts := newTestServer(t)
+	ts.bootstrap(t)
+	clientID := registerClient(t, ts, claudeCallback)
+	query := authorizeQuery(clientID, claudeCallback)
+
+	_, first := exchange(t, ts, codeForm(clientID, approve(t, ts, query)))
+	_, second := exchange(t, ts, codeForm(clientID, approve(t, ts, query)))
+
+	_, list := ts.do(t, "GET", "/api/v1/tokens", nil)
+	if n := len(list["tokens"].([]any)); n != 1 {
+		t.Errorf("tokens after reconnecting: %d, want 1", n)
+	}
+	if resp := mcpInitialize(t, ts, first["access_token"].(string)); resp.StatusCode != http.StatusUnauthorized {
+		t.Errorf("the replaced token still works: status %d", resp.StatusCode)
+	}
+	if resp := mcpInitialize(t, ts, second["access_token"].(string)); resp.StatusCode != http.StatusOK {
+		t.Errorf("the new token does not work: status %d", resp.StatusCode)
+	}
+}
+
+func jsonString(s string) string {
+	b, _ := json.Marshal(s)
+	return string(b)
+}

internal/httpapi/server.go

@@ -64,6 +64,10 @@ type Server struct {
 	// app_handlers.go.
 	wsTickets *wsTickets
 
+	// Authorization codes on their way to becoming an MCP client's token — see
+	// oauth_handlers.go.
+	oauthCodes *oauthCodes
+
 	// Password guessing is the attack this application is actually exposed to, so
 	// the endpoints that check a secret are limited separately and more tightly
 	// than the rest of the API.
@@ -73,6 +77,7 @@ type Server struct {
 	mailLimiter  *limiter
 	hookLimiter  *limiter
 	resetLimiter *limiter
+	oauthLimiter *limiter
 	// Second factors are counted against the *account*, not the address. An
 	// address bucket is defeated by anybody with more than one address, which is
 	// the ordinary case — and a six-digit code is only safe while guesses are
@@ -115,11 +120,16 @@ func New(cfg *config.Config, db *store.DB, log *slog.Logger, web fs.FS) *Server
 		mailLimiter:  newLimiter(60, time.Minute),
 		hookLimiter:  newLimiter(60, time.Minute),
 		resetLimiter: newLimiter(5, time.Hour),
+		// Registration and the token exchange are open to anybody who can reach
+		// the instance. A real client does each once per connection; thirty an
+		// hour is a ceiling nobody connecting meets.
+		oauthLimiter: newLimiter(30, time.Hour),
 		// Tighter than the password bucket, and for a whole hour. Somebody typing
 		// their own code gets it right on the first or second try; ten in an hour is
 		// generous for a person and hopeless for a search through a million.
 		totpLimiter: newLimiter(10, time.Hour),
 		wsTickets:   newWSTickets(),
+		oauthCodes:  newOAuthCodes(),
 	}
 	// Before the CSP, deliberately: the policy has to describe the bytes that go
 	// out, and in the notes edition those are the renamed ones.
@@ -259,6 +269,22 @@ func New(cfg *config.Config, db *store.DB, log *slog.Logger, web fs.FS) *Server
 	// nothing else.
 	r.Post("/mcp", s.handleMCPWithKey)
 
+	// Signing in to MCP with the account: discovery, registration, approval and
+	// the token exchange. In both editions, like the MCP server itself. None of
+	// them reads a cookie — the approval does, and it lives in /api/v1 below,
+	// behind the session and the CSRF check like every other write a browser
+	// makes. See oauth_handlers.go.
+	r.Get("/.well-known/oauth-protected-resource", s.handleProtectedResourceMetadata)
+	r.Get("/.well-known/oauth-protected-resource/mcp", s.handleProtectedResourceMetadata)
+	r.Get("/.well-known/oauth-authorization-server", s.handleAuthorizationServerMetadata)
+	r.Get("/oauth/authorize", s.handleOAuthAuthorize)
+	r.Options("/oauth/register", handleOpenPreflight)
+	r.Options("/oauth/token", handleOpenPreflight)
+	r.Method(http.MethodPost, "/oauth/register",
+		s.rateLimit(s.oauthLimiter, http.HandlerFunc(s.handleOAuthRegister)))
+	r.Method(http.MethodPost, "/oauth/token",
+		s.rateLimit(s.oauthLimiter, http.HandlerFunc(s.handleOAuthToken)))
+
 	// Google sends the browser here after consent. Outside /api/v1 because it is a
 	// top-level navigation rather than a fetch, but still behind the session — the
 	// tokens it exchanges belong to whoever is signed in.
@@ -458,6 +484,15 @@ func New(cfg *config.Config, db *store.DB, log *slog.Logger, web fs.FS) *Server
 				r.Delete("/{tokenID}", s.handleDeleteAPIToken)
 			})
 
+			// The approval page's two questions — what am I approving, and yes or
+			// no. Behind requireSession for the reason the tokens are: an approval
+			// mints a token.
+			r.Route("/oauth", func(r chi.Router) {
+				r.Use(s.requireSession)
+				r.Get("/request", s.handleOAuthRequest)
+				r.Post("/approve", s.handleOAuthApprove)
+			})
+
 			r.Route("/ai", func(r chi.Router) {
 				r.Get("/settings", s.handleGetAISettings)
 				r.Put("/settings", s.handleSetAISettings)
@@ -805,10 +840,9 @@ func (s *Server) serveWeb(w http.ResponseWriter, r *http.Request) {
 	//
 	// That is not hypothetical. Claude probes
 	// /.well-known/oauth-authorization-server before connecting to an MCP server,
-	// read 200 and a page of HTML as "there is an authorization server here", and
-	// then failed trying to register with it — reporting a broken sign-in service
-	// on a server that has none and needs none. A 404 means "no OAuth here", the
-	// client stops asking, and the key in the URL is used as intended.
+	// and before that path was a real route it read 200 and a page of HTML as
+	// "there is an authorization server here" and failed trying to register with
+	// it. The OAuth paths are routes now; everything else under here is a 404.
 	if strings.HasPrefix(r.URL.Path, "/.well-known/") {
 		writeJSON(w, http.StatusNotFound, map[string]string{"error": "not found"})
 		return

internal/httpapi/tokens_handlers.go

@@ -23,6 +23,9 @@ type apiTokenJSON struct {
 	CreatedAt  string `json:"created_at"`
 	LastUsedAt string `json:"last_used_at,omitempty"`
 	ExpiresAt  string `json:"expires_at,omitempty"`
+	// Connected is true for a token an app received by signing in (OAuth),
+	// rather than one made on this page.
+	Connected bool `json:"connected,omitempty"`
 }
 
 // createdTokenJSON is the only response that carries the token itself, and only
@@ -45,6 +48,7 @@ func (s *Server) handleListAPITokens(w http.ResponseWriter, r *http.Request) {
 		j := apiTokenJSON{
 			ID: t.ID, Name: t.Name, Prefix: t.Prefix,
 			CreatedAt: t.CreatedAt.Format(time.RFC3339),
+			Connected: t.Connected,
 		}
 		if t.LastUsedAt != nil {
 			j.LastUsedAt = t.LastUsedAt.Format(time.RFC3339)

internal/store/apitokens.go

@@ -17,6 +17,9 @@ type APIToken struct {
 	CreatedAt  time.Time
 	LastUsedAt *time.Time
 	ExpiresAt  *time.Time
+	// Connected marks a token an OAuth approval minted rather than one the
+	// person made by hand — it carries the client's name, not one they chose.
+	Connected bool
 }
 
 // CreateAPIToken returns the token in plaintext exactly once. Only its hash is
@@ -80,7 +83,8 @@ func (db *DB) UserByAPIToken(ctx context.Context, token string) (*User, error) {
 
 func (db *DB) ListAPITokens(ctx context.Context, userID string) ([]APIToken, error) {
 	rows, err := db.QueryContext(ctx,
-		`SELECT id, user_id, name, prefix, created_at, last_used_at, expires_at
+		`SELECT id, user_id, name, prefix, created_at, last_used_at, expires_at,
+		        oauth_client_id IS NOT NULL
 		 FROM api_tokens WHERE user_id = ? ORDER BY created_at DESC`, userID)
 	if err != nil {
 		return nil, err
@@ -92,7 +96,7 @@ func (db *DB) ListAPITokens(ctx context.Context, userID string) ([]APIToken, err
 		var t APIToken
 		var created int64
 		var lastUsed, expires sql.NullInt64
-		if err := rows.Scan(&t.ID, &t.UserID, &t.Name, &t.Prefix, &created, &lastUsed, &expires); err != nil {
+		if err := rows.Scan(&t.ID, &t.UserID, &t.Name, &t.Prefix, &created, &lastUsed, &expires, &t.Connected); err != nil {
 			return nil, err
 		}
 		t.CreatedAt = time.Unix(created, 0).UTC()

internal/store/migrations/0038_mcp_med_kontoen.sql

@@ -0,0 +1,29 @@
+-- At forbinde Claude med sin konto i stedet for med et token, man selv har lavet.
+--
+-- Claude's forbindelsesdialog prøver OAuth, før den gør noget andet, og indtil nu
+-- var svaret "det findes ikke her" — så den eneste vej ind var at lave et token i
+-- indstillingerne og sætte det ind i en adresse. Det virker, men det er en
+-- hemmelighed, man skal kopiere mellem to programmer, og det er præcis det trin,
+-- folk går i stå på.
+--
+-- En klient registrerer sig selv (RFC 7591) og får et id. Ingen hemmelighed: en
+-- klient, der kører hos en anden, kan ikke holde på en, så det er PKCE, der beviser,
+-- at det er den samme, der kommer tilbage med koden.
+CREATE TABLE oauth_clients (
+    id            TEXT PRIMARY KEY,
+    name          TEXT NOT NULL,
+    -- JSON-liste. Kun adresser, klienten selv opgav ved registreringen, kan få en
+    -- kode sendt hen til sig — ellers er "godkend" en knap, der sender adgangen til
+    -- hvem som helst.
+    redirect_uris TEXT NOT NULL,
+    created_at    INTEGER NOT NULL
+);
+
+-- Det, en godkendelse udsteder, er et almindeligt API-token. Det står derfor på
+-- siden med tokens, kan tilbagekaldes der, og når alle de steder, et token
+-- allerede gælder. Kolonnen siger, hvilken klient det hører til, så en ny
+-- godkendelse fra den samme klient erstatter den gamle frem for at lægge sig ved
+-- siden af.
+ALTER TABLE api_tokens ADD COLUMN oauth_client_id TEXT REFERENCES oauth_clients (id) ON DELETE CASCADE;
+
+CREATE INDEX idx_api_tokens_oauth_client ON api_tokens (oauth_client_id) WHERE oauth_client_id IS NOT NULL;

internal/store/oauth.go

@@ -0,0 +1,99 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"errors"
+	"time"
+
+	"github.com/kristianwind/verdande/internal/auth"
+)
+
+// OAuthClient is a program that registered itself to connect to an account: in
+// practice an MCP client such as Claude. It holds no secret — see migration 0038.
+type OAuthClient struct {
+	ID           string
+	Name         string
+	RedirectURIs []string
+	CreatedAt    time.Time
+}
+
+// unusedClientAge is how long a registration may sit without ever being
+// approved before it is cleared. Registration is open to anybody who can reach
+// the instance, so without this the table grows with every abandoned attempt.
+const unusedClientAge = 24 * time.Hour
+
+func (db *DB) CreateOAuthClient(ctx context.Context, name string, redirectURIs []string) (*OAuthClient, error) {
+	uris, err := json.Marshal(redirectURIs)
+	if err != nil {
+		return nil, err
+	}
+	c := &OAuthClient{ID: NewID(), Name: name, RedirectURIs: redirectURIs, CreatedAt: time.Now().UTC()}
+
+	// Swept on the way in, like the socket tickets: the table is bounded by a
+	// day of asking, and nothing has to remember to run a job for it.
+	_, _ = db.ExecContext(ctx,
+		`DELETE FROM oauth_clients WHERE created_at < ?
+		 AND NOT EXISTS (SELECT 1 FROM api_tokens WHERE oauth_client_id = oauth_clients.id)`,
+		time.Now().Add(-unusedClientAge).Unix())
+
+	_, err = db.ExecContext(ctx,
+		`INSERT INTO oauth_clients (id, name, redirect_uris, created_at) VALUES (?, ?, ?, ?)`,
+		c.ID, c.Name, string(uris), c.CreatedAt.Unix())
+	if err != nil {
+		return nil, err
+	}
+	return c, nil
+}
+
+func (db *DB) OAuthClient(ctx context.Context, id string) (*OAuthClient, error) {
+	var c OAuthClient
+	var uris string
+	var created int64
+	err := db.QueryRowContext(ctx,
+		`SELECT id, name, redirect_uris, created_at FROM oauth_clients WHERE id = ?`, id).
+		Scan(&c.ID, &c.Name, &uris, &created)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal([]byte(uris), &c.RedirectURIs); err != nil {
+		return nil, err
+	}
+	c.CreatedAt = time.Unix(created, 0).UTC()
+	return &c, nil
+}
+
+// CreateOAuthToken mints the API token an approval hands to a client.
+//
+// Any earlier token this person gave the same client is deleted in the same
+// transaction. A client that connects again — after a reinstall, or because
+// somebody pressed "connect" twice — then has one entry on the tokens page
+// rather than a growing column of identical ones, each still valid.
+func (db *DB) CreateOAuthToken(ctx context.Context, userID string, client *OAuthClient) (string, error) {
+	token, prefix, err := auth.NewAPIToken()
+	if err != nil {
+		return "", err
+	}
+
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return "", err
+	}
+	defer tx.Rollback()
+
+	if _, err := tx.ExecContext(ctx,
+		`DELETE FROM api_tokens WHERE user_id = ? AND oauth_client_id = ?`, userID, client.ID); err != nil {
+		return "", err
+	}
+	if _, err := tx.ExecContext(ctx,
+		`INSERT INTO api_tokens (id, user_id, name, token_hash, prefix, created_at, oauth_client_id)
+		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
+		NewID(), userID, client.Name, auth.HashToken(token), prefix, time.Now().Unix(), client.ID); err != nil {
+		return "", err
+	}
+	return token, tx.Commit()
+}

web/e2e/smoke.spec.js

@@ -1,4 +1,5 @@
 import { test, expect } from '@playwright/test';
+import { createHash } from 'node:crypto';
 import { USER } from './user.js';
 import { watchForTrouble } from './trouble.js';
 
@@ -6168,3 +6169,78 @@ test('en titel, der rettes i opgaveruden, tager gentagelse, tid, projekt og alar
 	const { reminders } = await apiCall(page, 'GET', `/tasks/${task.id}/reminders`);
 	expect(reminders.map((r) => r.offset_min)).toEqual([-60]);
 });
+
+/**
+ * At forbinde Claude med kontoen: hele dansen, som Claude danser den, med den
+ * eneste del, en Go-prøve ikke kan se — at godkendelsessiden findes, logger én
+ * ind, når det trænges, og at "Tillad" faktisk sender browseren tilbage med en
+ * kode, der kan veksles til et token, som /mcp tager imod.
+ *
+ * Tilbageadressen er en fremmed vært, som prøven selv svarer for. En rigtig
+ * claude.ai ville gøre prøven afhængig af nettet og af en side, vi ikke ejer.
+ */
+test('Claude kan forbinde med kontoen i stedet for med et token', async ({ page, browser }) => {
+	const callback = 'https://claude.example/api/mcp/auth_callback';
+	const registered = await page.request.post('/oauth/register', {
+		data: { client_name: 'Claude', redirect_uris: [callback], token_endpoint_auth_method: 'none' }
+	});
+	expect(registered.status()).toBe(201);
+	const { client_id } = await registered.json();
+
+	// S256 af en fast nøgle. Regnet i Node: en tom side er ikke en sikker
+	// kontekst, så browserens crypto.subtle findes ikke der.
+	const verifier = 'v'.repeat(43);
+	const challenge = createHash('sha256').update(verifier).digest('base64url');
+
+	const query = new URLSearchParams({
+		response_type: 'code', client_id, redirect_uri: callback, state: 'tilstand',
+		code_challenge: challenge, code_challenge_method: 'S256'
+	}).toString();
+
+	// Uden en session: login-skærmen, på godkendelsessidens adresse, så man
+	// lander tilbage på spørgsmålet bagefter.
+	// Tom storageState: browser.newContext() i en prøve arver projektets, og
+	// projektets er en logget-ind konto.
+	const stranger = await browser.newContext({ storageState: { cookies: [], origins: [] } });
+	const signedOut = await stranger.newPage();
+	await signedOut.goto('/oauth/authorize?' + query);
+	await expect(signedOut.getByLabel('E-mail')).toBeVisible();
+	expect(new URL(signedOut.url()).pathname).toBe('/forbind');
+	await stranger.close();
+
+	let returned = null;
+	await page.route('https://claude.example/**', (route) => {
+		returned = new URL(route.request().url());
+		return route.fulfill({ status: 200, contentType: 'text/plain', body: 'ok' });
+	});
+
+	await page.goto('/oauth/authorize?' + query);
+	await expect(page.getByRole('heading', { name: 'Claude vil forbinde til din konto' })).toBeVisible();
+	// Hvor koden sendes hen er det, en klient ikke kan lyve om — det skal stå der.
+	await expect(page.getByText('claude.example', { exact: true })).toBeVisible();
+
+	await page.getByRole('button', { name: 'Tillad' }).click();
+	await expect.poll(() => returned?.searchParams.get('code') ?? null).not.toBeNull();
+	expect(returned.searchParams.get('state')).toBe('tilstand');
+
+	const exchanged = await page.request.post('/oauth/token', {
+		form: {
+			grant_type: 'authorization_code', code: returned.searchParams.get('code'),
+			client_id, redirect_uri: callback, code_verifier: verifier
+		}
+	});
+	expect(exchanged.status()).toBe(200);
+	const { access_token } = await exchanged.json();
+	expect(access_token).toMatch(/^vrd_/);
+
+	const mcp = await page.request.post('/mcp', {
+		headers: { Authorization: 'Bearer ' + access_token },
+		data: { jsonrpc: '2.0', id: 1, method: 'initialize', params: {} }
+	});
+	expect(mcp.status()).toBe(200);
+	expect((await mcp.json()).result.protocolVersion).toBeTruthy();
+
+	// Og den står under Tokens, hvor den kan tilbagekaldes.
+	await page.goto('/indstillinger/tokens');
+	await expect(page.getByText('forbundet med din konto')).toBeVisible();
+});

web/src/lib/api.js

@@ -445,6 +445,12 @@ export const api = {
 		post('/tokens', { name, expires_in_days: expiresInDays ?? 0 }),
 	deleteToken: (id) => del(`/tokens/${id}`),
 
+	// --- signing an MCP client in with the account (routes/forbind)
+	// The query goes over unchanged: the server reads it with the same function
+	// that checked it on the way in, so the two cannot disagree about it.
+	oauthRequest: (query) => get(`/oauth/request${query}`),
+	oauthApprove: (query, approve) => post('/oauth/approve', { query, approve }),
+
 	// --- live sync, for the app (see stores.svelte.js)
 	wsTicket: () => post('/ws-ticket'),
 

web/src/lib/locales/da.js

@@ -498,6 +498,20 @@ export const da = {
 	'ai.keyNewHint': 'Gemmes på serveren og vises aldrig igen.',
 	'tokens.lastUsed': 'sidst brugt {when}',
 	'tokens.neverUsed': 'aldrig brugt',
+	'connect.title': 'Forbind',
+	'connect.heading': '{name} vil forbinde til din konto',
+	'connect.what': 'Den kan læse og ændre dine opgaver og noter — med præcis dine rettigheder, ikke flere.',
+	'connect.whatNotes': 'Den kan læse og ændre dine noter — med præcis dine rettigheder, ikke flere.',
+	'tokens.signInHint': 'Til Claude og andre MCP-programmer behøver du ikke et token: tilføj adressen nedenfor som forbindelse, og log ind, når programmet beder om det.',
+	'connect.account': 'Konto',
+	'connect.sentTo': 'Sendes til',
+	'connect.revoke': 'Du kan afbryde forbindelsen når som helst under Indstillinger → Tokens.',
+	'connect.allow': 'Tillad',
+	'connect.deny': 'Afvis',
+	'connect.brokenTitle': 'Forbindelsen kan ikke laves',
+	'connect.broken': 'Programmet, der sendte dig hertil, bad om noget, der ikke kan godkendes. Fjern forbindelsen i programmet, og tilføj den igen.',
+	'connect.toApp': 'Til appen',
+	'tokens.connected': 'forbundet med din konto',
 	'tokens.expired': 'udløbet {when}',
 	'tokens.expiresOn': 'udløber {when}',
 	'tokens.revokeNamed': 'Tilbagekald {name}',

web/src/lib/locales/en.js

@@ -492,6 +492,20 @@ export const en = {
 	'ai.keyNewHint': 'Stored on the server and never shown again.',
 	'tokens.lastUsed': 'last used {when}',
 	'tokens.neverUsed': 'never used',
+	'connect.title': 'Connect',
+	'connect.heading': '{name} wants to connect to your account',
+	'connect.what': 'It can read and change your tasks and notes — with exactly your permissions, no more.',
+	'connect.whatNotes': 'It can read and change your notes — with exactly your permissions, no more.',
+	'tokens.signInHint': 'Claude and other MCP programs do not need a token: add the address below as a connector, and sign in when it asks.',
+	'connect.account': 'Account',
+	'connect.sentTo': 'Sent to',
+	'connect.revoke': 'You can disconnect it at any time under Settings → Tokens.',
+	'connect.allow': 'Allow',
+	'connect.deny': 'Deny',
+	'connect.brokenTitle': 'This connection cannot be made',
+	'connect.broken': 'The program that sent you here asked for something that cannot be approved. Remove the connection in that program and add it again.',
+	'connect.toApp': 'To the app',
+	'tokens.connected': 'connected with your account',
 	'tokens.expired': 'expired {when}',
 	'tokens.expiresOn': 'expires {when}',
 	'tokens.revokeNamed': 'Revoke {name}',

web/src/routes/+layout.svelte

@@ -52,8 +52,12 @@
 	 * screen. Without this the invite link showed a login form to a person who had
 	 * no account yet, and the reset link showed one to a person who had forgotten
 	 * the password it was asking for.
+	 *
+	 * `/forbind` is the third: the screen an MCP client sends somebody to. It
+	 * signs them in itself and then asks one question, and the shell around it
+	 * would be a way to wander off before answering it.
 	 */
-	let standalone = $derived(['/invite', '/reset'].includes($page.url.pathname));
+	let standalone = $derived(['/invite', '/reset', '/forbind'].includes($page.url.pathname));
 
 	$effect(() => {
 		app.load();

web/src/routes/forbind/+page.svelte

@@ -0,0 +1,224 @@
+<script>
+	/**
+	 * The approval screen an MCP client sends somebody to: "Claude wants to
+	 * connect to your account".
+	 *
+	 * The server's /oauth/authorize checks the request and hands the browser
+	 * here with the query unchanged. Signing in, if it is needed, is the ordinary
+	 * sign-in screen — passkeys and second factor included — and this page takes
+	 * over once there is somebody to ask.
+	 *
+	 * Two things are shown, and only one of them can be trusted. The name is
+	 * whatever the client called itself when it registered: any program can call
+	 * itself Claude. Where the browser goes afterwards is the address the client
+	 * registered, and that is what decides who receives the access — so it is
+	 * shown, and shown as plainly as the name.
+	 */
+	import SignIn from '$lib/components/SignIn.svelte';
+	import { api, humanMessage } from '$lib/api.js';
+	import { app } from '$lib/stores.svelte.js';
+	import { t } from '$lib/i18n.svelte.js';
+
+	const query = typeof location === 'undefined' ? '' : location.search;
+
+	/** @type {{ client_name: string, redirect_to: string } | null} */
+	let request = $state(null);
+	let problem = $state('');
+	let busy = $state(false);
+
+	$effect(() => {
+		if (!app.user || request || problem) return;
+		api
+			.oauthRequest(query)
+			.then((r) => (request = r))
+			.catch((e) => (problem = e.message || humanMessage(e)));
+	});
+
+	async function answer(approve) {
+		busy = true;
+		try {
+			const { redirect_to } = await api.oauthApprove(query, approve);
+			// The server only ever answers with an address the client registered,
+			// and refuses the schemes a browser would run. Checked again here
+			// because this line is what hands it to the browser.
+			const scheme = new URL(redirect_to).protocol;
+			if (['javascript:', 'data:', 'vbscript:', 'blob:'].includes(scheme)) throw new Error('bad redirect');
+			location.assign(redirect_to);
+		} catch (e) {
+			busy = false;
+			app.toast(humanMessage(e));
+		}
+	}
+</script>
+
+<svelte:head><title>{t('connect.title')} · {app.productSlug}</title></svelte:head>
+
+{#if !app.user}
+	<SignIn />
+{:else}
+	<div class="screen">
+		<div class="card">
+			<div class="brand">
+				<span class="rune" aria-hidden="true">ᚹ</span>
+				<span class="slug">{app.productSlug}</span>
+			</div>
+
+			{#if problem}
+				<h1>{t('connect.brokenTitle')}</h1>
+				<p class="lede">{t('connect.broken')}</p>
+				<p class="detail mono">{problem}</p>
+				<a class="link" href="/">{t('connect.toApp')}</a>
+			{:else if !request}
+				<p class="lede">…</p>
+			{:else}
+				<h1>{t('connect.heading', { name: request.client_name })}</h1>
+				<p class="lede">{t(app.notesOnly ? 'connect.whatNotes' : 'connect.what')}</p>
+
+				<dl>
+					<dt>{t('connect.account')}</dt>
+					<dd>{app.user.name} · {app.user.email}</dd>
+					<dt>{t('connect.sentTo')}</dt>
+					<dd class="mono">{request.redirect_to}</dd>
+				</dl>
+
+				<p class="hint">{t('connect.revoke')}</p>
+
+				<div class="actions">
+					<button class="allow" disabled={busy} onclick={() => answer(true)}>{t('connect.allow')}</button>
+					<button class="deny" disabled={busy} onclick={() => answer(false)}>{t('connect.deny')}</button>
+				</div>
+			{/if}
+		</div>
+	</div>
+{/if}
+
+<style>
+	.screen {
+		min-height: 100dvh;
+		display: grid;
+		place-items: center;
+		padding: var(--s4);
+		background: var(--ground);
+	}
+
+	.card {
+		width: 100%;
+		max-width: 380px;
+		display: flex;
+		flex-direction: column;
+		gap: var(--s4);
+	}
+
+	.brand {
+		display: flex;
+		align-items: center;
+		gap: var(--s3);
+		justify-content: center;
+	}
+
+	.rune {
+		font-size: var(--text-2xl);
+		color: var(--accent);
+		line-height: 1;
+	}
+
+	.slug {
+		font-size: var(--text-lg);
+		font-weight: 560;
+	}
+
+	h1 {
+		margin: 0;
+		font-size: var(--text-xl);
+		font-weight: 560;
+		letter-spacing: -0.02em;
+		text-align: center;
+		text-wrap: balance;
+	}
+
+	.lede {
+		margin: 0;
+		text-align: center;
+		color: var(--ink-muted);
+		font-size: var(--text-sm);
+	}
+
+	dl {
+		margin: 0;
+		padding: var(--s3) var(--s4);
+		display: grid;
+		grid-template-columns: auto 1fr;
+		gap: var(--s2) var(--s4);
+		background: var(--surface);
+		border: 1px solid var(--line);
+		border-radius: var(--radius);
+		font-size: var(--text-sm);
+	}
+
+	dt {
+		color: var(--ink-faint);
+	}
+
+	dd {
+		margin: 0;
+		min-width: 0;
+		overflow-wrap: anywhere;
+		color: var(--ink);
+	}
+
+	.mono {
+		font-family: var(--font-mono);
+	}
+
+	.hint,
+	.detail {
+		margin: 0;
+		font-size: var(--text-xs);
+		color: var(--ink-faint);
+		text-align: center;
+		overflow-wrap: anywhere;
+	}
+
+	.actions {
+		display: flex;
+		flex-direction: column;
+		gap: var(--s2);
+	}
+
+	.allow {
+		padding: var(--s3);
+		background: var(--accent);
+		color: var(--accent-ink);
+		border-radius: var(--radius);
+		font-weight: 550;
+		transition: background var(--fast) var(--ease);
+	}
+
+	.allow:hover:not(:disabled) {
+		background: var(--accent-hover);
+	}
+
+	.deny {
+		padding: var(--s2) var(--s4);
+		border: 1px solid var(--line-strong);
+		border-radius: var(--radius);
+		font-size: var(--text-sm);
+		color: var(--ink);
+	}
+
+	button:disabled {
+		opacity: 0.6;
+		cursor: default;
+	}
+
+	.link {
+		color: var(--ink-faint);
+		font-size: var(--text-sm);
+		text-align: center;
+		text-decoration: none;
+	}
+
+	.link:hover {
+		color: var(--ink);
+	}
+</style>

web/src/routes/indstillinger/tokens/+page.svelte

@@ -99,6 +99,10 @@
 		<p class="hint">
 			{t('tokens.hint')}
 		</p>
+		<!-- The way most people want: no token at all. The address is the same
+		     for everybody on this instance, so it can be shown without a secret. -->
+		<p class="hint">{t('tokens.signInHint')}</p>
+		<p class="mono value">{location.origin}/mcp</p>
 	</header>
 
 	{#if fresh}
@@ -175,6 +179,7 @@
 						<span class="token-name">{token.name}</span>
 						<span class="meta mono">
 							{token.prefix}…
+							{#if token.connected}· {t('tokens.connected')}{/if}
 							{#if token.last_used_at}
 								· {t('tokens.lastUsed', { when: date(token.last_used_at) })}
 							{:else}