Add support for OAuth 2.0 Client Authentication via JWT (RFC 7523)

[mridang]

Add support for OAuth 2.0 Client Authentication via JWT (RFC 7523)

Description:

The SDK currently supports personal access token (PAT) authentication. To
expand authentication options, we need to implement OAuth 2.0 Client
Authentication using JWTs (RFC 7523). This would allow clients to authenticate
using JWTs for OAuth 2.0 access token requests and client authentication.

RFC 7523 Authentication:

• JWT Bearer Token: Used as a means for client authentication when requesting
  OAuth 2.0 access tokens and as an authorization grant.

Tasks:

• Implement JWT-based client authentication to request OAuth 2.0 tokens as per RFC
  7523.
• Add support for the client_assertion parameter in OAuth requests for client
  authentication.
• Implement error handling for invalid JWTs and failed client authentication.
• Update SDK to document the JWT client authentication process.

Expected Outcomes:

• OAuth 2.0 authentication should support client authentication with JWTs.
• Backward compatibility with existing authentication methods (PAT).
• Clear documentation for the JWT-based client authentication flow.

Additional Notes:

• Consider using libraries like to handle JWT creation and
  validation.
• Ensure the security of the JWTs, including proper signing and verification
  mechanisms.