add supabase-auth

[aaazzam]

Description

Add Supabase authentication provider for FastMCP following the same pattern as existing commercial auth providers (Auth0, Descope, WorkOS).

The SupabaseProvider implements RemoteAuthProvider to verify JWTs issued by Supabase Auth using their JWKS endpoint. It supports Supabase projects using
asymmetric ES256 signing keys (standard for projects created after May 2025, or migrated projects).

Key Features:

• JWT verification using Supabase's JWKS endpoint (/auth/v1/.well-known/jwks.json)
• ES256 algorithm support (Elliptic Curve Digital Signature)
• Environment variable configuration (FASTMCP_SERVER_AUTH_SUPABASE_*)
• Authorization server metadata forwarding
• Follows established FastMCP auth provider patterns

Testing:

• Validated end-to-end with real Supabase project
• Successfully authenticated users and verified JWTs
• Protected MCP endpoints working correctly

🤖 Generated with https://claude.com/claude-code

Contributors Checklist

• My change closes Support Supabase Auth Provider. #1996
• I have followed the repository's development workflow
• I have tested my changes manually and by adding relevant tests
• I have performed all required documentation updates

Review Checklist

• I have self-reviewed my changes
• My Pull Request is ready for review

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Files Changed:

• src/fastmcp/server/auth/providers/supabase.py - Provider implementation
• tests/server/auth/providers/test_supabase.py - Comprehensive test suite (9 tests)

[jlowin]

Think the only thing missing here is an integration doc in the style of other auth integrations (which we can also generate subsequently if you want)