Configure an NSURLSession so that it will load HTTPS even from servers with invalid TLS certificate

NSURLSessionAllowBadCertificateDelegate.swift

// works as of Swift 1.2, 2015-08-29

// https://developer.apple.com/library/ios/technotes/tn2232/_index.html#//apple_ref/doc/uid/DTS40012884-CH1-SECNSURLSESSION

class NSURLSessionAllowBadCertificateDelegate : NSObject, NSURLSessionDelegate
{
  func URLSession(session: NSURLSession, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential!) -> Void)
  {
    if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust
    {
      let trustObject = challenge.protectionSpace.serverTrust
      let credential = NSURLCredential(forTrust: challenge.protectionSpace.serverTrust)
      completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential,credential)
    }
    else {
      completionHandler(NSURLSessionAuthChallengeDisposition.PerformDefaultHandling,nil)
    }
  }
}

let session = NSURLSession(
  configuration: NSURLSessionConfiguration.ephemeralSessionConfiguration(),
  delegate: NSURLSessionAllowBadCertificateDelegate(),
  delegateQueue: nil)