Support Client Auth Certificate in OIDCTokenRequest Endpoint

OIDC Providers support multiple options to request for Token with authorization code . Current implement only supports ClientSecret. Requesting to add support for 2 way SSL Client Support by enabling one more additional parameter . So that we have an option to use either ClientSecret or 2 way SSL Token Request Call.

Start by locating the OIDCTokenRequest endpoint and the existing ClientSecret token-request handling in the Go plugin. Trace how the endpoint builds its authorization-code token request, then determine the configuration and request path needed to support client-certificate authentication alongside ClientSecret. Done means either authentication option can be used successfully.

Written by the indexing model from the issue text.