NSURLSessionDataDelegate didReceiveChallenge callback not called in ios 8

Question

I am using NSURLSession to create an https network call. But below, callback is not called in ios 8, but the same callback works in ios 7 / ios 7.1. Are there any changes in ios 8 related to this.

public func URLSession(session: NSURLSession, task: NSURLSessionTask, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential!) -> Void) {