modelcontextprotocol / modelcontextprotocol/python-sdk
Bug: validate_scope rejects client scopes when required scopes in None
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Description
Initial Checks
- I confirm that I'm using the latest version of MCP Python SDK
- I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue
Description
The validate_scope() function in the Python SDK incorrectly handles cases where there are no required scopes from the client. Instead of treating None as no restrictions, it interprets it as an empty list of allowed scopes. This causes scopes in the token to be rejected with InvalidScopeError, even if the client should be allowed to request them.
Example Code
Python & MCP Python SDK
1.26.0
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Locate validate_scope in the Python SDK and trace how required scopes are handled when the value is None. Reproduce the case with client scopes absent and token scopes present, then verify that valid scopes are no longer rejected with InvalidScopeError and add coverage for the behavior.
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Assessment
- Tech stack
- python
- Domain
- authentication, authorization
- Issue type
- Bug
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 64/100