Add a standardized OAuth 2.1-based authentication specification for MCP
sub-registries, aligned with the MCP Authorization Specification.
This enables:
- Private registry entries with access control
- Permission-based server visibility
- Client code reuse (clients can use their existing MCP auth
implementation)
The spec is intended for downstream sub-registries. The official
registry remains public for reading.
Fixes#751
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Co-authored-by: Claude <noreply@anthropic.com>
