OAuth handler doesn't support redirect URLs with params
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Assessment
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Newbie friendliness
- 78/100
- Issue type
- Bug
- Clarity
- Clearly specified
- Activity status
- Active
- Tech stack
- python
- Domain
- authentication
Research direction
Start in src/mcp/client/auth/oauth2.py at lines 356-357, where the authorization URL is assembled before redirect_handler is called. Check how the server-provided endpoint and authorization parameters are joined. Done means endpoints that already contain query parameters produce a valid URL with both the existing and newly added parameters.
Written by the indexing model from the issue text.
Description
Initial Checks
- I confirm that I'm using the latest version of MCP Python SDK
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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 & MCP Python SDK
python3 3.13.2
mcp 1.27.2
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