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Foundation Framework Reference NSURLAuthenticationChallenge Class Reference

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NSURLAuthenticationChallenge

NSURLAuthenticationChallenge encapsulates a challenge from a server requiring authentication from the client.

Most apps do not create authentication challenges themselves. However, you might need to create authentication challenge objects when adding support for custom networking protocols, as part of your custom NSURLProtocol subclasses.

Instead, your app receives authentication challenges in various NSURLSession, NSURLConnection, and NSURLDownload delegate methods, such as URLSession:task:didReceiveChallenge:completionHandler:. These objects provide the information you’ll need when deciding how to handle a server’s request for authentication. At the core of that authentication challenge is a protection space that defines the type of authentication being requested, the host and port number, the networking protocol, and (where applicable) the authentication realm (a group of related URLs on the same server that share a single set of credentials).

Your app responds to authentication challenges by providing an NSURLCredential object. The details depend on the API you are using and on the type of challenge.

At a high level, if you’re providing the user’s credentials to a server or proxy, the proposedCredential method provides a credential that matches the criteria specified in the protection space, retrieved from the NSURLCredentialStorage class handling the request (assuming such a credential exists).

If the previousFailureCount method returns 0 and the proposed credential exists, the proposed credential has not yet been tried, which means you should try it. If it returns a nonzero result, then the server has rejected the proposed credential, and you should use that credential to populate a password or certificate chooser dialog, then provide a new credential. You can create password-based credentials by calling the credentialWithUser:password:persistence: method or create certificate-based credentials with the credentialWithIdentity:certificates:persistence:.

If the authentication’s protection space uses the NSURLAuthenticationMethodServerTrust authentication method, the request is asking you to verify the server’s authenticity. In this case, the proposedCredential method provides a credential based on the certificates that the server provided as part of its initial TLS handshake. Most apps should request default handling for authentication challenges based on a server trust protection space, but if you need to override the default TLS validation behavior, you can do so as described in Overriding TLS Chain Validation Correctly.

For more information about how URL sessions handle the different types of authentication challenges, see NSURLSession Class Reference and URL Session Programming Guide.

  • The error object representing the last authentication failure. (read-only)

    Declaration

    Swift

    @NSCopying var error: NSError? { get }

    Objective-C

    @property(readonly, copy) NSError *error

    Discussion

    This method returns nil if the protocol doesn’t use errors to indicate an authentication failure.

    Availability

    Available in iOS 2.0 and later.

  • The URL response object representing the last authentication failure. (read-only)

    Declaration

    Swift

    @NSCopying var failureResponse: NSURLResponse? { get }

    Objective-C

    @property(readonly, copy) NSURLResponse *failureResponse

    Discussion

    This method returns nil if the protocol doesn’t use responses to indicate an authentication failure.

    Availability

    Available in iOS 2.0 and later.

    See Also

    – error

  • The receiver’s count of failed authentication attempts. (read-only)

    Declaration

    Swift

    var previousFailureCount: Int { get }

    Objective-C

    @property(readonly) NSInteger previousFailureCount

    Discussion

    The previous failure count includes failures from all protection spaces, not just the current one.

    Availability

    Available in iOS 2.0 and later.

  • The proposed credential for this challenge. (read-only)

    Declaration

    Swift

    @NSCopying var proposedCredential: NSURLCredential? { get }

    Objective-C

    @property(readonly, copy) NSURLCredential *proposedCredential

    Discussion

    This method returns nil if there is no default credential for this challenge.

    If you have previously attempted to authenticate and failed, this method returns the most recent failed credential.

    If the proposed credential is not nil and returns YEStrue when you call its hasPassword method, then the credential is ready to use as-is. If the proposed credential’s hasPassword method returns NOfalse, then the credential provides a default user name, and the client must prompt the user for a corresponding password.

    Availability

    Available in iOS 2.0 and later.

  • The receiver’s protection space. (read-only)

    Declaration

    Swift

    @NSCopying var protectionSpace: NSURLProtectionSpace { get }

    Objective-C

    @property(readonly, copy) NSURLProtectionSpace *protectionSpace

    Discussion

    A protection space object provides additional information about the authentication request, such as the host, port, authentication realm, and so on. The protection space also tells you whether the authentication challenge is asking you to provide the user’s credentials or to verify the TLS credentials provided by the server.

    Availability

    Available in iOS 2.0 and later.

  • The receiver’s sender.

    Declaration

    Swift

    var sender: NSURLAuthenticationChallengeSender? { get }

    Objective-C

    @property(readonly, retain) id< NSURLAuthenticationChallengeSender > sender

    Discussion

    The sender is typically an instance of an NSURLProtocol subclass that initially received the authentication challenge.

    If you are using the NSURLSession API, this value is purely informational, because you must respond to authentication challenges by passing constants to the provided completion handler blocks.

    However, if you are using the NSURLConnection or NSURLDownload API, in your authentication handler delegate method, you respond to authentication challenges by calling methods defined in the NSURLAuthenticationChallengeSender protocol on this sender object after you finish processing the authentication challenge.

    Availability

    Available in iOS 2.0 and later.