Session.swift

fileprivate class SessionDelegate: NSObject, URLSessionDelegate {

    // MARK: - NSURLSessionDelegate

    public func urlSession(_ session: URLSession,
                           didReceive challenge: URLAuthenticationChallenge,
                           completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?)
        -> Void) {

        if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust &&
            Constants.selfSignedHosts.contains(challenge.protectionSpace.host) {

            let credential = URLCredential(trust: challenge.protectionSpace.serverTrust!)
            completionHandler(.useCredential, credential)
        } else {

            completionHandler(.performDefaultHandling, nil)
        }
    }

    struct Constants {
        // A list of hosts you allow self-signed certificates on.
        // You'd likely have your dev/test servers here.
        // Please don't put your production server here!
        static let selfSignedHosts: Set<String> = []
    }
}

extension URLSession {

    static var sessionDefault: URLSession {
        return URLSession(
            configuration: URLSessionConfiguration.sessionConfiguration(),
            delegate: SessionDelegate(),
            delegateQueue: OperationQueue.main)
    }
}

fileprivate extension URLSessionConfiguration {

    fileprivate class func sessionConfiguration() -> URLSessionConfiguration {
        let config = ephemeral
        config.timeoutIntervalForRequest = 20 // Make things timeout quickly.
        config.httpShouldUsePipelining = true // Might speed things up if your server supports it.
        return config
    }
}