feat(passport): Enhance the client authentication methods for token exchange

[betimshahini]

Our current support is limited to the equivalent of the client_secret_post authentication type for the purpose of authenticating a client at the token exchange stage of the authz flow.

Additional methods should be supported. References:

• https://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication
• https://datatracker.ietf.org/doc/html/draft-ietf-oauth-security-topics#name-client-authentication

This ticket tracks:

• [ ] Feature and design decision
• [ ] Breakdown of implementation work.