Implementation of TrustedCallbackInterface. Solution used can be found at...
Implementation of TrustedCallbackInterface. Solution used can be found at https://drupal.stackexchange.com/questions/307757/how-to-implement-trustedcallbackinterface
Implementation of TrustedCallbackInterface. Solution used can be found at https://drupal.stackexchange.com/questions/307757/how-to-implement-trustedcallbackinterface