final OAuth2AuthorizationGrantBuilder delegate() {
        return delegate;
    }
A common abstraction for the requests implementing various Access Token request/response flows,
as per <a href="https://datatracker.ietf.org/doc/rfc6749/">[RFC6749]</a>.

@param accessTokenEndpoint A {@link WebClient} to facilitate an Access Token request. Must correspond to
                           the Access Token endpoint of the OAuth 2 system.
@param accessTokenEndpointPath A URI path that corresponds to the Access Token endpoint of the
                               OAuth 2 system.
oauth2/src/main/java/com/linecorp/armeria/client/auth/oauth2/AbstractOAuth2AuthorizationGrantBuilder.java