accessTokenHttpResponseConverter and errorHttpResponseConverter allow custom

[luamas]

gh-1058

[jgrandja]

@luamas We do not want to expose HttpMessageConverter<OAuth2AccessTokenResponse> or HttpMessageConverter<OAuth2Error>. The main extension points for customizing the access token response and error response are AuthenticationSuccessHandler and AuthenticationFailureHandler.

Please see this comment for further details.

Also, for future reference, please log the issue first and let's discuss the proposal to see if it will be accepted or not. This will avoid any unnecessary work. Thank you.