This PR implements authorization support as per RFC 9728 (#686).
It introduces robust token generation and validation methods, fully aligned with the new MCP authorization specification.
The changes include:
Implementation of token generation using JWT with proper encoding and expiration.
Validation of JWT tokens with issuer and audience verification.
Error handling for expired or invalid tokens.
Unit tests for token generation, validation, claim extraction, and expiration scenarios.

Motivation and Context

The primary motivation for this change is to ensure MCP Python SDK’s compliance with RFC 9728, the new authorization specification.
By adding proper token management, it
*Enhances security by leveraging JWT-based authentication.
*Aligns with the authorization standards outlined in the MCP specification.
*Provides a robust framework for secure client-server communication.
*This change addresses Issue #686 by implementing the authorization flow, including token creation, validation, and handling edge cases like expiration and invalid claims.

How Has This Been Tested?

*All unit tests have been executed and passed successfully, covering the following scenarios:
*Generating a valid token and verifying its claims.
*Detecting an expired token.
*Extracting a specific claim from a valid token.
*Handling a token with invalid claims.

Handling a completely invalid or malformed token.

Breaking Changes

None.
The introduced features are additive and do not affect existing functionality.

Types of changes

• 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 change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

This feature aligns the MCP Python SDK with the latest authorization standards as outlined in RFC 9728.
It also improves security practices by ensuring token validity and proper claim extraction in a structured and standardized way.