# NSURLProtectionSpace authentication method constants Constants describing known values of the [`authenticationMethod`](/documentation/Foundation/URLProtectionSpace/authenticationMethod) property of a [`URLProtectionSpace`](/documentation/Foundation/URLProtectionSpace). ## Discussion These constants are also used with the [`URLProtectionSpace`](/documentation/Foundation/URLProtectionSpace) initializers [`init(host:port:protocol:realm:authenticationMethod:)`](/documentation/Foundation/URLProtectionSpace/init(host:port:protocol:realm:authenticationMethod:)) and [`init(proxyHost:port:type:realm:authenticationMethod:)`](/documentation/Foundation/URLProtectionSpace/init(proxyHost:port:type:realm:authenticationMethod:)). ## Topics ### Session-wide authentication challenges These constants indicate session-wide challenges. Delegates handle these challenges in the [`URLSessionDelegate`](/documentation/Foundation/URLSessionDelegate) A protocol that defines methods that URL session instances call on their delegates to handle session-level events, like session life cycle changes. method [`- URLSession:didReceiveChallenge:completionHandler:`](/documentation/Foundation/URLSessionDelegate/urlSession(_:didReceive:completionHandler:)) Requests credentials from the delegate in response to a session-level authentication request from the remote server.. [`NSURLAuthenticationMethodClientCertificate`](/documentation/Foundation/NSURLAuthenticationMethodClientCertificate) Use client certificate authentication for this protection space. [`NSURLAuthenticationMethodNegotiate`](/documentation/Foundation/NSURLAuthenticationMethodNegotiate) Negotiate whether to use Kerberos or NTLM authentication for this protection space. [`NSURLAuthenticationMethodNTLM`](/documentation/Foundation/NSURLAuthenticationMethodNTLM) Use NTLM authentication for this protection space. [`NSURLAuthenticationMethodServerTrust`](/documentation/Foundation/NSURLAuthenticationMethodServerTrust) Perform server trust authentication (certificate validation) for this protection space. ### Task-specific authentication challenges These constants indicate task-specific challenges. Delegates handle these challenges in the [`URLSessionTaskDelegate`](/documentation/Foundation/URLSessionTaskDelegate) A protocol that defines methods that URL session instances call on their delegates to handle task-level events. method [`- URLSession:task:didReceiveChallenge:completionHandler:`](/documentation/Foundation/URLSessionTaskDelegate/urlSession(_:task:didReceive:completionHandler:)) Requests credentials from the delegate in response to an authentication request from the remote server.. [`NSURLAuthenticationMethodDefault`](/documentation/Foundation/NSURLAuthenticationMethodDefault) Use the default authentication method for a protocol. [`NSURLAuthenticationMethodHTMLForm`](/documentation/Foundation/NSURLAuthenticationMethodHTMLForm) Use HTML form authentication for this protection space. [`NSURLAuthenticationMethodHTTPBasic`](/documentation/Foundation/NSURLAuthenticationMethodHTTPBasic) Use HTTP basic authentication for this protection space. [`NSURLAuthenticationMethodHTTPDigest`](/documentation/Foundation/NSURLAuthenticationMethodHTTPDigest) Use HTTP digest authentication for this protection space. ## See Also [Handling an authentication challenge](/documentation/Foundation/handling-an-authentication-challenge) Respond appropriately when a server demands authentication for a URL request. [Performing manual server trust authentication](/documentation/Foundation/performing-manual-server-trust-authentication) Evaluate the server’s security credentials in your app. --- 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)