René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"OAuth handler doesn't support redirect URLs with params","articleBody":"### Initial Checks\n\n- [x] I confirm that I'm using the latest version of MCP Python SDK\n- [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue\n\n### Description\n\nThe 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:\n```\n        authorization_url = f\"{auth_endpoint}?{urlencode(auth_params)}\"\n        await self.context.redirect_handler(authorization_url)\n```\n\nUnfortunately, 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.\n\nThe 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\u0026..., which is incorrect.\n\n### Example Code\n\n```Python\n\n```\n\n### Python \u0026 MCP Python SDK\n\n```Text\npython3 3.13.2\nmcp 1.27.2\n```","author":{"url":"https://github.com/artdent","@type":"Person","name":"artdent"},"datePublished":"2026-06-03T22:39:05.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/2776/python-sdk/issues/2776"}