Если вы используете NSURLConnection для подключения к вашему серверу, вам следует реализовать следующие методы в вашем делегате:
- (BOOL)connection:(NSURLConnection *)conn canAuthenticateAgainstProtectionSpace:(NSURLProtectionSpace *)protectionSpace;
// A delegate method called by the NSURLConnection when something happens with the
// connection security-wise. We defer all of the logic for how to handle this to
// the ChallengeHandler module (and it's very custom subclasses).
- (void)connection:(NSURLConnection *)conn didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge
// A delegate method called by the NSURLConnection when you accept a specific
// authentication challenge by returning YES from -connection:canAuthenticateAgainstProtectionSpace:.
// Again, most of the logic has been shuffled off to the ChallengeHandler module; the only
// policy decision we make here is that, if the challenge handle doesn't get it right in 5 tries,
// we bail out.
Я советую вам просмотреть этот пример от Apple: Расширенные соединения с URL