fix: surface OAuth token persistence failures

Author: he-yufeng

.changeset/forty-mayflies-tease.md

@@ -0,0 +1,5 @@
+---
+"@modelcontextprotocol/client": patch
+---
+
+fix(client): surface OAuth token persistence failures

packages/client/src/client/auth.ts

@@ -763,19 +763,17 @@ async function authInternal(
 
     // Handle token refresh or new authorization
     if (tokens?.refresh_token) {
+        let newTokens: OAuthTokens | undefined;
         try {
             // Attempt to refresh the token
-            const newTokens = await refreshAuthorization(authorizationServerUrl, {
+            newTokens = await refreshAuthorization(authorizationServerUrl, {
                 metadata,
                 clientInformation,
                 refreshToken: tokens.refresh_token,
                 resource,
                 addClientAuthentication: provider.addClientAuthentication,
                 fetchFn
             });
-
-            await provider.saveTokens(newTokens);
-            return 'AUTHORIZED';
         } catch (error) {
             // If this is a ServerError, or an unknown type, log it out and try to continue. Otherwise, escalate so we can fix things and retry.
             if (!(error instanceof OAuthError) || error.code === OAuthErrorCode.ServerError) {
@@ -785,6 +783,11 @@ async function authInternal(
                 throw error;
             }
         }
+
+        if (newTokens !== undefined) {
+            await provider.saveTokens(newTokens);
+            return 'AUTHORIZED';
+        }
     }
 
     const state = provider.state ? await provider.state() : undefined;

packages/client/test/client/auth.test.ts

@@ -2591,6 +2591,73 @@ describe('OAuth Authorization', () => {
             expect(body.get('refresh_token')).toBe('refresh123');
         });
 
+        it('does not hide token persistence failures after refresh succeeds', async () => {
+            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']
+                        })
+                    });
+                } 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']
+                        })
+                    });
+                } else if (urlString.includes('/token')) {
+                    return Promise.resolve({
+                        ok: true,
+                        status: 200,
+                        json: async () => ({
+                            access_token: 'new-access123',
+                            token_type: 'Bearer',
+                            expires_in: 3600,
+                            refresh_token: 'new-refresh123'
+                        })
+                    });
+                }
+
+                return Promise.resolve({ ok: false, status: 404 });
+            });
+
+            const saveError = new Error('token store unavailable');
+            (mockProvider.clientInformation as Mock).mockResolvedValue({
+                client_id: 'test-client',
+                client_secret: 'test-secret'
+            });
+            (mockProvider.tokens as Mock).mockResolvedValue({
+                access_token: 'old-access',
+                refresh_token: 'refresh123'
+            });
+            (mockProvider.saveTokens as Mock).mockRejectedValue(saveError);
+
+            await expect(
+                auth(mockProvider, {
+                    serverUrl: 'https://api.example.com/mcp-server'
+                })
+            ).rejects.toThrow('token store unavailable');
+
+            expect(mockProvider.saveTokens).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    access_token: 'new-access123',
+                    refresh_token: 'new-refresh123'
+                })
+            );
+            expect(mockProvider.redirectToAuthorization).not.toHaveBeenCalled();
+        });
+
         it('skips default PRM resource validation when custom validateResourceURL is provided', async () => {
             const mockValidateResourceURL = vi.fn().mockResolvedValue(undefined);
             const providerWithCustomValidation = {