code: public Request<UserInfo> userInfo(String accessToken) {
          Asserts.assertNotNull(accessToken, "access token");
  
          String url = baseUrl
                  .newBuilder()
                  .addPathSegment("userinfo")
                  .build()
                  .toString();
          CustomRequest<UserInfo> request = new CustomRequest<>(client, url, "GET", new TypeReference<UserInfo>() {
          });
          request.addHeader("Authorization", "Bearer " + accessToken);
          return request;
      }
docs: Request the user information related to the access token.
  i.e.:
  <pre>
  {@code
  AuthAPI auth = new AuthAPI("me.auth0.com", "B3c6RYhk1v9SbIJcRIOwu62gIUGsnze", "2679NfkaBn62e6w5E8zNEzjr-yWfkaBne");
  try {
  UserInfo result = auth.userInfo("A9CvPwFojaBIA9CvI").execute();
  } catch (Auth0Exception e) {
  //Something happened
  }
  }
  </pre>
  
  @param accessToken a valid access token belonging to an API signed with RS256 algorithm and containing the scope 'openid'.
  @return a Request to execute.