func webView(_ webView: WKWebView, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {     var error: CFError?     if #available(iOS 12.0, *) { dispatch_semaphore_t sema = dispatch_semaphore_create(0); // Multiple requests may come to load into web view     self.pinningCompletion = completionHandler; // strong property       DebugLog(tag: TAG, info: "WebView: didReceive challenge - ios12 or higher")       if let trust = challenge.protectionSpace.serverTrust, !SecTrustEvaluateWithError(trust, &error) {         // OK         let ok = UIAlertAction(title: "OK", style: .default) { _ in           let exceptions = SecTrustCopyExceptions(trust)           SecTrustSetExceptions(trust, exceptions)           completionHandler(.useCredential, URLCredential(trust: trust))   dispatch_semaphore_signal(sema);// on completion of alert action         }         // Cancel         let cancel = UIAlertAction(title: "Cancel", style: .cancel) { _ in           completionHandler(.cancelAuthenticationChallenge, nil)   dispatch_semaphore_signal(sema);// on completion of alert action         }         // Show prompt         let message = error!.localizedDescription + "\nDo you want to continue?"         let alert = UIAlertController(title: "SSL Error", message: message, preferredStyle: .alert)         alert.addAction(ok)         alert.addAction(cancel)         DispatchQueue.main.async {           self.present(alert, animated: true, completion: nil)         }  if (![NSThread isMainThread]) {             dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);         } else {             while (dispatch_semaphore_wait(sema, DISPATCH_TIME_NOW)) {                 [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:0]];             }         }       }       else {         let cred = URLCredential(trust: challenge.protectionSpace.serverTrust!)         completionHandler(.useCredential, cred)       }     } else {       DebugLog(tag: TAG, info: "WebView: didReceive challenge - fallback older versions")       let cred = URLCredential(trust: challenge.protectionSpace.serverTrust!)       completionHandler(.useCredential, cred)     }   }