🛂 refactor: Use discoverAuthorizationServerMetadata for MCP OAuth

[jhrozek]

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Summary

Uses the discoverAuthorizationServerMetadata function from the upstream
TS SDK. This has the advantage of falling back to OIDC discovery
metadata if the OAuth discovery metadata doesn't exist which is the case
with e.g. keycloak.

Change Type

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Translation update

Testing

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Test Configuration:

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• Any changes dependent on mine have been merged and published in downstream modules.
• A pull request for updating the documentation has been submitted.