Add refresh token support defaults to GoogleProvider

Set access_type=offline and prompt=consent by default to ensure
refresh tokens are returned by Google. Also expose extra_authorize_params
so users can customize authorization behavior.

src/fastmcp/server/auth/providers/google.py

@@ -225,6 +225,7 @@ class GoogleProvider(OAuthProxy):
         client_storage: AsyncKeyValue | None = None,
         jwt_signing_key: str | bytes | NotSetT = NotSet,
         require_authorization_consent: bool = True,
+        extra_authorize_params: dict[str, str] | None = None,
     ):
         """Initialize Google OAuth provider.
 
@@ -252,6 +253,10 @@ class GoogleProvider(OAuthProxy):
                 When True, users see a consent screen before being redirected to Google.
                 When False, authorization proceeds directly without user confirmation.
                 SECURITY WARNING: Only disable for local development or testing environments.
+            extra_authorize_params: Additional parameters to forward to Google's authorization endpoint.
+                By default, GoogleProvider sets {"access_type": "offline", "prompt": "consent"} to ensure
+                refresh tokens are returned. You can override these defaults or add additional parameters.
+                Example: {"prompt": "select_account"} to let users choose their Google account.
         """
 
         settings = GoogleProviderSettings.model_validate(
@@ -299,6 +304,18 @@ class GoogleProvider(OAuthProxy):
             settings.client_secret.get_secret_value() if settings.client_secret else ""
         )
 
+        # Set Google-specific defaults for extra authorize params
+        # access_type=offline ensures refresh tokens are returned
+        # prompt=consent forces consent screen to get refresh token (Google only issues on first auth otherwise)
+        google_defaults = {
+            "access_type": "offline",
+            "prompt": "consent",
+        }
+        # User-provided params override defaults
+        if extra_authorize_params:
+            google_defaults.update(extra_authorize_params)
+        extra_authorize_params_final = google_defaults
+
         # Initialize OAuth proxy with Google endpoints
         super().__init__(
             upstream_authorization_endpoint="https://accounts.google.com/o/oauth2/v2/auth",
@@ -314,6 +331,7 @@ class GoogleProvider(OAuthProxy):
             client_storage=client_storage,
             jwt_signing_key=settings.jwt_signing_key,
             require_authorization_consent=require_authorization_consent,
+            extra_authorize_params=extra_authorize_params_final,
         )
 
         logger.debug(

tests/server/auth/providers/test_google.py

@@ -119,3 +119,46 @@ class TestGoogleProvider:
 
         # Provider should initialize successfully with these scopes
         assert provider is not None
+
+    def test_extra_authorize_params_defaults(self):
+        """Test that Google-specific defaults are set for refresh token support."""
+        provider = GoogleProvider(
+            client_id="123456789.apps.googleusercontent.com",
+            client_secret="GOCSPX-test123",
+            jwt_signing_key="test-secret",
+        )
+
+        # Should have Google-specific defaults for refresh token support
+        assert provider._extra_authorize_params == {
+            "access_type": "offline",
+            "prompt": "consent",
+        }
+
+    def test_extra_authorize_params_override_defaults(self):
+        """Test that user can override default extra authorize params."""
+        provider = GoogleProvider(
+            client_id="123456789.apps.googleusercontent.com",
+            client_secret="GOCSPX-test123",
+            jwt_signing_key="test-secret",
+            extra_authorize_params={"prompt": "select_account"},
+        )
+
+        # User override should replace the default
+        assert provider._extra_authorize_params["prompt"] == "select_account"
+        # But other defaults should remain
+        assert provider._extra_authorize_params["access_type"] == "offline"
+
+    def test_extra_authorize_params_add_new_params(self):
+        """Test that user can add additional authorize params."""
+        provider = GoogleProvider(
+            client_id="123456789.apps.googleusercontent.com",
+            client_secret="GOCSPX-test123",
+            jwt_signing_key="test-secret",
+            extra_authorize_params={"login_hint": "user@example.com"},
+        )
+
+        # New param should be added
+        assert provider._extra_authorize_params["login_hint"] == "user@example.com"
+        # Defaults should still be present
+        assert provider._extra_authorize_params["access_type"] == "offline"
+        assert provider._extra_authorize_params["prompt"] == "consent"