public JSONObject register(String username, String password, String email) {
   try {
     return api.registerUser(username, password, email);
   } catch (HttpException e) {
     e.printStackTrace();
   }
   Log.i(TAG, "Register call Login API error!");
   return null;
 }
 public JSONObject login(String email, String password) {
   try {
     return api.userLogin(email, password);
   } catch (ResponseException e) {
     e.printStackTrace();
   } catch (HttpException e) {
     e.printStackTrace();
   }
   Log.i(TAG, "User call Login API error!");
   return null;
 }