feat: use scopes_supported from resource metadata by default (fixes #580)

Author: antogyn

src/client/auth.test.ts

@@ -10,7 +10,7 @@ import {
   auth,
   type OAuthClientProvider,
 } from "./auth.js";
-import { OAuthMetadata } from '../shared/auth.js';
+import { OAuthClientMetadata, OAuthMetadata, OAuthProtectedResourceMetadata } from '../shared/auth.js';
 
 // Mock fetch globally
 const mockFetch = jest.fn();
@@ -926,6 +926,48 @@ describe("OAuth Authorization", () => {
       );
     });
 
+    it("registers client with scopes_supported from resourceMetadata if scope is not provided", async () => {
+      const resourceMetadata: OAuthProtectedResourceMetadata = {
+        scopes_supported: ["openid", "profile"],
+        resource: "https://api.example.com/mcp-server",
+      };
+
+      const validClientMetadataWithoutScope: OAuthClientMetadata = {
+        ...validClientMetadata,
+        scope: undefined,
+      };
+
+      const expectedClientInfo = {
+        ...validClientInfo,
+        scope: "openid profile",
+      };
+
+      mockFetch.mockResolvedValueOnce({
+        ok: true,
+        status: 200,
+        json: async () => expectedClientInfo,
+      });
+
+      const clientInfo = await registerClient("https://auth.example.com", {
+        clientMetadata: validClientMetadataWithoutScope,
+        resourceMetadata,
+      });
+
+      expect(clientInfo).toEqual(expectedClientInfo);
+      expect(mockFetch).toHaveBeenCalledWith(
+        expect.objectContaining({
+          href: "https://auth.example.com/register",
+        }),
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+          },
+          body: JSON.stringify({ ...validClientMetadata, scope: "openid profile" }),
+        })
+      );
+    });
+
     it("validates client information response schema", async () => {
       mockFetch.mockResolvedValueOnce({
         ok: true,
@@ -1266,6 +1308,64 @@ describe("OAuth Authorization", () => {
       expect(body.get("refresh_token")).toBe("refresh123");
     });
 
+    it("uses scopes_supported from resource metadata if scope is not provided", async () => {
+      // Mock successful metadata discovery - need to include protected resource metadata
+      mockFetch.mockImplementation((url) => {
+        const urlString = url.toString();
+        if (urlString.includes("/.well-known/oauth-protected-resource")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: async () => ({
+              resource: "https://api.example.com/mcp-server",
+              authorization_servers: ["https://auth.example.com"],
+              scopes_supported: ["openid", "profile"],
+            }),
+          });
+        } else if (urlString.includes("/.well-known/oauth-authorization-server")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: async () => ({
+              issuer: "https://auth.example.com",
+              authorization_endpoint: "https://auth.example.com/authorize",
+              token_endpoint: "https://auth.example.com/token",
+              response_types_supported: ["code"],
+              code_challenge_methods_supported: ["S256"],
+            }),
+          });
+        }
+        return Promise.resolve({ ok: false, status: 404 });
+      });
+
+      // Mock provider methods for authorization flow
+      (mockProvider.clientInformation as jest.Mock).mockResolvedValue({
+        client_id: "test-client",
+        client_secret: "test-secret",
+      });
+      (mockProvider.tokens as jest.Mock).mockResolvedValue(undefined);
+      (mockProvider.saveCodeVerifier as jest.Mock).mockResolvedValue(undefined);
+      (mockProvider.redirectToAuthorization as jest.Mock).mockResolvedValue(undefined);
+
+      // Call auth without authorization code (should trigger redirect)
+      const result = await auth(mockProvider, {
+        serverUrl: "https://api.example.com/mcp-server",
+      });
+
+      expect(result).toBe("REDIRECT");
+
+      // Verify the authorization URL includes the resource parameter
+      expect(mockProvider.redirectToAuthorization).toHaveBeenCalledWith(
+        expect.objectContaining({
+          searchParams: expect.any(URLSearchParams),
+        })
+      );
+
+      const redirectCall = (mockProvider.redirectToAuthorization as jest.Mock).mock.calls[0];
+      const authUrl: URL = redirectCall[0];
+      expect(authUrl.searchParams.get("scope")).toBe("openid profile");
+    });
+
     it("skips default PRM resource validation when custom validateResourceURL is provided", async () => {
       const mockValidateResourceURL = jest.fn().mockResolvedValue(undefined);
       const providerWithCustomValidation = {

src/client/auth.ts

@@ -235,12 +235,13 @@ export async function auth(
     serverUrl: string | URL;
     authorizationCode?: string;
     scope?: string;
-    resourceMetadataUrl?: URL }): Promise<AuthResult> {
+    resourceMetadataUrl?: URL
+  }): Promise<AuthResult> {
 
   let resourceMetadata: OAuthProtectedResourceMetadata | undefined;
   let authorizationServerUrl = serverUrl;
   try {
-    resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, {resourceMetadataUrl});
+    resourceMetadata = await discoverOAuthProtectedResourceMetadata(serverUrl, { resourceMetadataUrl });
     if (resourceMetadata.authorization_servers && resourceMetadata.authorization_servers.length > 0) {
       authorizationServerUrl = resourceMetadata.authorization_servers[0];
     }
@@ -265,6 +266,7 @@ export async function auth(
 
     const fullInformation = await registerClient(authorizationServerUrl, {
       metadata,
+      resourceMetadata,
       clientMetadata: provider.clientMetadata,
     });
 
@@ -318,7 +320,7 @@ export async function auth(
     clientInformation,
     state,
     redirectUrl: provider.redirectUrl,
-    scope: scope || provider.clientMetadata.scope,
+    scope: (scope || provider.clientMetadata.scope) ?? resourceMetadata?.scopes_supported?.join(" "),
     resource,
   });
 
@@ -761,9 +763,11 @@ export async function registerClient(
   authorizationServerUrl: string | URL,
   {
     metadata,
+    resourceMetadata,
     clientMetadata,
   }: {
     metadata?: OAuthMetadata;
+    resourceMetadata?: OAuthProtectedResourceMetadata;
     clientMetadata: OAuthClientMetadata;
   },
 ): Promise<OAuthClientInformationFull> {
@@ -779,12 +783,17 @@ export async function registerClient(
     registrationUrl = new URL("/register", authorizationServerUrl);
   }
 
+  const scope = clientMetadata?.scope ?? resourceMetadata?.scopes_supported?.join(" ");
+
   const response = await fetch(registrationUrl, {
     method: "POST",
     headers: {
       "Content-Type": "application/json",
     },
-    body: JSON.stringify(clientMetadata),
+    body: JSON.stringify({
+      ...clientMetadata,
+      ...(scope !== undefined ? { scope } : undefined)
+    }),
   });
 
   if (!response.ok) {