switchMap(() => {
                /**
                 * Native HTTP Cordova plugin doesn't like local requests
                 */
                const isExternalRequest = checkExternalRequest(req);

                if (
                    isExternalRequest &&
                    checkAvailability('cordova.plugin.http') === true
                ) {
                    return this.cordovaHttpBackend.handle(req);
                } else {
                    return this.fallbackBackend.handle(req);
                }
            }),

 protected delegate(request: HttpRequest<any>): Observable<HttpEvent<any>> {
   return this.backend.handle(request);
 }