code: public AuthorizationRequestUrl setResponseTypes(Collection<String> responseTypes) {
      this.responseTypes = Joiner.on(' ').join(responseTypes);
      return this;
    }
docs: Sets the <a href="http://tools.ietf.org/html/rfc6749#section-3.1.1">response type</a>, which
  must be {@code "code"} for requesting an authorization code, {@code "token"} for requesting an
  access token (implicit grant), or a list of registered extension values to join with a space.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>
  
  @since 1.15