Adds support for private_key_jwt
Created by: SteveyblamWork
A recent merge added support for tls_client_auth scheme by providing an auth scheme value that would only add the client_id to the request body. The Private Key JWT scheme includes the client_id in the client_assertion and so is not needed in the main request body.
This PR simply returns unaltered params when private_key_jwt is specified as the auth_scheme