refactor(auth): remove unused _register_client method (#1748)

src/mcp/client/auth/oauth2.py

@@ -19,7 +19,7 @@ import anyio
 import httpx
 from pydantic import BaseModel, Field, ValidationError
 
-from mcp.client.auth.exceptions import OAuthFlowError, OAuthRegistrationError, OAuthTokenError
+from mcp.client.auth.exceptions import OAuthFlowError, OAuthTokenError
 from mcp.client.auth.utils import (
     build_oauth_authorization_server_metadata_discovery_urls,
     build_protected_resource_metadata_discovery_urls,
@@ -299,44 +299,6 @@ class OAuthClientProvider(httpx.Auth):
                 f"Protected Resource Metadata request failed: {response.status_code}"
             )  # pragma: no cover
 
-    async def _register_client(self) -> httpx.Request | None:
-        """Build registration request or skip if already registered."""
-        if self.context.client_info:
-            return None
-
-        if self.context.oauth_metadata and self.context.oauth_metadata.registration_endpoint:
-            registration_url = str(self.context.oauth_metadata.registration_endpoint)  # pragma: no cover
-        else:
-            auth_base_url = self.context.get_authorization_base_url(self.context.server_url)
-            registration_url = urljoin(auth_base_url, "/register")
-
-        registration_data = self.context.client_metadata.model_dump(by_alias=True, mode="json", exclude_none=True)
-
-        # If token_endpoint_auth_method is None, auto-select based on server support
-        if self.context.client_metadata.token_endpoint_auth_method is None:
-            preference_order = ["client_secret_basic", "client_secret_post", "none"]
-
-            if self.context.oauth_metadata and self.context.oauth_metadata.token_endpoint_auth_methods_supported:
-                supported = self.context.oauth_metadata.token_endpoint_auth_methods_supported
-                for method in preference_order:
-                    if method in supported:
-                        registration_data["token_endpoint_auth_method"] = method
-                        break
-                else:
-                    # No compatible methods between client and server
-                    raise OAuthRegistrationError(
-                        f"No compatible authentication methods. "
-                        f"Server supports: {supported}, "
-                        f"Client supports: {preference_order}"
-                    )
-            else:
-                # No server metadata available, use our default preference
-                registration_data["token_endpoint_auth_method"] = preference_order[0]
-
-        return httpx.Request(
-            "POST", registration_url, json=registration_data, headers={"Content-Type": "application/json"}
-        )
-
     async def _perform_authorization(self) -> httpx.Request:
         """Perform the authorization flow."""
         auth_code, code_verifier = await self._perform_authorization_code_grant()

tests/client/test_auth.py

@@ -3,7 +3,6 @@ Tests for refactored OAuth client authentication implementation.
 """
 
 import base64
-import json
 import time
 from unittest import mock
 from urllib.parse import unquote
@@ -13,7 +12,7 @@ import pytest
 from inline_snapshot import Is, snapshot
 from pydantic import AnyHttpUrl, AnyUrl
 
-from mcp.client.auth import OAuthClientProvider, OAuthRegistrationError, PKCEParameters
+from mcp.client.auth import OAuthClientProvider, PKCEParameters
 from mcp.client.auth.utils import (
     build_oauth_authorization_server_metadata_discovery_urls,
     build_protected_resource_metadata_discovery_urls,
@@ -581,98 +580,6 @@ class TestOAuthFallback:
         # Verify that scope is omitted
         assert scopes is None
 
-    @pytest.mark.anyio
-    async def test_register_client_request(self, oauth_provider: OAuthClientProvider):
-        """Test client registration request building."""
-        request = await oauth_provider._register_client()
-
-        assert request is not None
-        assert request.method == "POST"
-        assert str(request.url) == "https://api.example.com/register"
-        assert request.headers["Content-Type"] == "application/json"
-
-    @pytest.mark.anyio
-    async def test_register_client_skip_if_registered(self, oauth_provider: OAuthClientProvider):
-        """Test client registration is skipped if already registered."""
-        # Set existing client info
-        client_info = OAuthClientInformationFull(
-            client_id="existing_client",
-            redirect_uris=[AnyUrl("http://localhost:3030/callback")],
-        )
-        oauth_provider.context.client_info = client_info
-
-        # Should return None (skip registration)
-        request = await oauth_provider._register_client()
-        assert request is None
-
-    @pytest.mark.anyio
-    async def test_register_client_explicit_auth_method(self, mock_storage: MockTokenStorage):
-        """Test that explicitly set token_endpoint_auth_method is used without auto-selection."""
-
-        async def redirect_handler(url: str) -> None:
-            pass  # pragma: no cover
-
-        async def callback_handler() -> tuple[str, str | None]:
-            return "test_auth_code", "test_state"  # pragma: no cover
-
-        # Create client metadata with explicit auth method
-        explicit_metadata = OAuthClientMetadata(
-            client_name="Test Client",
-            client_uri=AnyHttpUrl("https://example.com"),
-            redirect_uris=[AnyUrl("http://localhost:3030/callback")],
-            scope="read write",
-            token_endpoint_auth_method="client_secret_basic",
-        )
-        provider = OAuthClientProvider(
-            server_url="https://api.example.com/v1/mcp",
-            client_metadata=explicit_metadata,
-            storage=mock_storage,
-            redirect_handler=redirect_handler,
-            callback_handler=callback_handler,
-        )
-
-        request = await provider._register_client()
-        assert request is not None
-
-        body = json.loads(request.content)
-        # Should use the explicitly set method, not auto-select
-        assert body["token_endpoint_auth_method"] == "client_secret_basic"
-
-    @pytest.mark.anyio
-    async def test_register_client_none_auth_method_with_server_metadata(self, oauth_provider: OAuthClientProvider):
-        """Test that token_endpoint_auth_method=None selects from server's supported methods."""
-        # Set server metadata with specific supported methods
-        oauth_provider.context.oauth_metadata = OAuthMetadata(
-            issuer=AnyHttpUrl("https://auth.example.com"),
-            authorization_endpoint=AnyHttpUrl("https://auth.example.com/authorize"),
-            token_endpoint=AnyHttpUrl("https://auth.example.com/token"),
-            token_endpoint_auth_methods_supported=["client_secret_post"],
-        )
-        # Ensure client_metadata has None for token_endpoint_auth_method
-
-        request = await oauth_provider._register_client()
-        assert request is not None
-
-        body = json.loads(request.content)
-        assert body["token_endpoint_auth_method"] == "client_secret_post"
-
-    @pytest.mark.anyio
-    async def test_register_client_none_auth_method_no_compatible(self, oauth_provider: OAuthClientProvider):
-        """Test that registration raises error when no compatible auth methods."""
-        # Set server metadata with unsupported methods only
-        oauth_provider.context.oauth_metadata = OAuthMetadata(
-            issuer=AnyHttpUrl("https://auth.example.com"),
-            authorization_endpoint=AnyHttpUrl("https://auth.example.com/authorize"),
-            token_endpoint=AnyHttpUrl("https://auth.example.com/token"),
-            token_endpoint_auth_methods_supported=["private_key_jwt", "client_secret_jwt"],
-        )
-
-        with pytest.raises(OAuthRegistrationError) as exc_info:
-            await oauth_provider._register_client()
-
-        assert "No compatible authentication methods" in str(exc_info.value)
-        assert "private_key_jwt" in str(exc_info.value)
-
     @pytest.mark.anyio
     async def test_token_exchange_request_authorization_code(self, oauth_provider: OAuthClientProvider):
         """Test token exchange request building."""