code: public <C extends Credentials, U extends CommonProfile> Auth client(
        final Function<Config, Client<C, U>> provider) {
      return client("*", provider);
    }
docs: Add an auth client, like facebook, twitter, github, etc...Please note the require dependency
  must be in the classpath.
  
  @param provider Client to add.
  @param <C> Credentials.
  @param <U> CommonProfile.
  @return This module.