### Initial Checks - [x] I confirm that I'm using the latest version of MCP Python SDK - [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue ### Description The oauth redirect handler uses the following logic (https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/auth/oauth2.py#L356-L357) to attach parameters to the redirect URL supplied by the server: ``` authorization_url = f"{auth_endpoint}?{urlencode(auth_params)}" await self.context.redirect_handler(authorization_url) ``` Unfortunately, this breaks if the auth_endpoint supplied by the server already has URL parameters. For example, at https://api.salesforce.com/.well-known/oauth-authorization-server/platform/mcp/v1/sandbox/platform/sobject-all you can see that the salesforce mcp server has an authorization endpoint of https://test.salesforce.com/services/oauth2/authorize?prompt=select_account. The end result is that the client tries to visit a URL that loooks like https://test.salesforce.com/services/oauth2/authorize?prompt=select_account?response_type=code&..., which is incorrect. ### Example Code ```Python ``` ### Python & MCP Python SDK ```Text python3 3.13.2 mcp 1.27.2 ```
Initial Checks
Description
The oauth redirect handler uses the following logic (https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/auth/oauth2.py#L356-L357) to attach parameters to the redirect URL supplied by the server:
Unfortunately, this breaks if the auth_endpoint supplied by the server already has URL parameters. For example, at https://api.salesforce.com/.well-known/oauth-authorization-server/platform/mcp/v1/sandbox/platform/sobject-all you can see that the salesforce mcp server has an authorization endpoint of https://test.salesforce.com/services/oauth2/authorize?prompt=select_account.
The end result is that the client tries to visit a URL that loooks like https://test.salesforce.com/services/oauth2/authorize?prompt=select_account?response_type=code&..., which is incorrect.
Example Code
Python & MCP Python SDK