# init(authenticationChallenge:sender:) Creates an authentication challenge from an existing challenge instance. ``` init(authenticationChallenge challenge: URLAuthenticationChallenge, sender: any URLAuthenticationChallengeSender) ``` ## Parameters `challenge` The challenge that you want to copy. Usually, this is a challenge received by an existing [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass that you are subclassing. `sender` The sender that you want to use for the new object. Typically, the sender is the instance of your custom [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass that called this method. ## Return Value A new authentication challenge object, based on an existing challenge. ## Discussion Most apps don’t create [`URLAuthenticationChallenge`](/documentation/Foundation/URLAuthenticationChallenge) instances themselves. Instead, they handle received challenges in the [`urlSession(_:task:didReceive:completionHandler:)`](/documentation/Foundation/URLSessionTaskDelegate/urlSession(_:task:didReceive:completionHandler:)) method of [`URLSessionTaskDelegate`](/documentation/Foundation/URLSessionTaskDelegate). However, you might need to create authentication challenge objects when adding support for custom networking protocols, as part of a custom [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass. When you subclass an existing [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass, this initializer lets you modify challenges issued by the existing class so that your subclass receives any responses to those challenges. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)