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

    if challenge.previousFailureCount > 0 {
        println("Alert Please check the credential")
        completionHandler(NSURLSessionAuthChallengeDisposition.CancelAuthenticationChallenge, nil)
    } else {
        var credential = NSURLCredential(user:"username", password:"password", persistence: .ForSession)
        completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential,credential)
    }
}

completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential,credential)