The current (and default) implementation of OAuth2AccessTokenResponseClient for the authorization_code grant is NimbusAuthorizationCodeTokenResponseClient, which leverages the Nimbus HTTP Client internally.

We should provide a new implementation of OAuth2AccessTokenResponseClient for the authorization_code grant named DefaultAuthorizationCodeTokenResponseClient that uses RestOperations for requesting to the Token Endpoint.

Additionally, DefaultAuthorizationCodeTokenResponseClient should expose setRestOperations(restOperations) method to allow user's the ability to supply a pre-configured RestOperations, which can provide the user the capability to add custom parameters and/or headers if required.

DefaultAuthorizationCodeTokenResponseClient should be the new default in OAuth2LoginConfigurer and OAuth2ClientConfigurer.

Related #5601