Swift SSL error with self signed certificate

@Ashish Kakkad was spot on. This works:

class Blah: NSURLSessionDelegate {

    func rest() {
        let path = "https://localhost:8443/greeting"
        let request = NSMutableURLRequest(URL: NSURL(string: path)!)
        let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
        let session = NSURLSession(configuration: configuration, delegate: self, delegateQueue:NSOperationQueue.mainQueue())
        let task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
            let json:JSON = JSON(data: data!)
            if let c = json["content"].string {
                print(c)
            }
        })
        task.resume()
    }

    func URLSession(session: NSURLSession, task: NSURLSessionTask, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential?) -> Void) {
        completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential, NSURLCredential(forTrust: challenge.protectionSpace.serverTrust!))
    }
}

With this in the Info.plist file:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>localhost</key>
        <dict>
            <key>NSExceptionAllowsInsecureHTTPLoads</key>
            <true/>
        </dict>
    </dict>
</dict>

you can use your own certificates instead of my certificates(fullchain.pem)

    class AccessingServer: NSObject,URLSessionDelegate {

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

        if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
            // First load our extra root-CAs to be trusted from the app bundle.
            let trust = challenge.protectionSpace.serverTrust

            let rootCa = "fullchain"
            if let rootCaPath = Bundle.main.path(forResource: rootCa, ofType: "pem") {
                if let rootCaData = NSData(contentsOfFile: rootCaPath) {

                    let rootCert = SecCertificateCreateWithData(nil, rootCaData)!

                    SecTrustSetAnchorCertificates(trust!, [rootCert] as CFArray)

                    SecTrustSetAnchorCertificatesOnly(trust!, false)
                }
            }

            var trustResult: SecTrustResultType = SecTrustResultType.invalid
            SecTrustEvaluate(trust!, &trustResult)

            if (trustResult == SecTrustResultType.unspecified ||
                trustResult == SecTrustResultType.proceed) {
                // Trust certificate.

                let credential = URLCredential(trust: challenge.protectionSpace.serverTrust!)
                challenge.sender?.use(credential, for: challenge)

            } else {
                NSLog("Invalid server certificate.")
                challenge.sender?.cancel(challenge)
            }
        } else {
            NSLog("Got unexpected authentication method \(challenge.protectionSpace.authenticationMethod)");
            challenge.sender?.cancel(challenge)
        }
    }

   }

Sai Reddy's solution allows you to accept your self-signed certificate if it has a complete chain, but it also accepts others.

Marcus Leon's solution is a complete override -- basically ignoring all certificates.

I like this one better.

Swift 4.1, iOS 11.4.1

First, in your Info.plist:

<key>NSAppTransportSecurity</key>
    <dict>
        <key>NSAllowsArbitraryLoads</key>
        <true/>
    </dict>

Second, wherever you use your NSURLSession, instead of setting up with URLSession.shared, use something like this:

session = URLSession(configuration: .default, delegate: APIURLSessionTaskDelegate(isSSLPinningEnabled: isSSLPinningEnabled), delegateQueue: nil)

Then add this class to handle pinning:

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

        print("*** received SESSION challenge...\(challenge)")
        let trust = challenge.protectionSpace.serverTrust!
        let credential = URLCredential(trust: trust)

        guard isSSLPinningEnabled else {
            print("*** SSL Pinning Disabled -- Using default handling.")
            completionHandler(.useCredential, credential)
            return
        }

        let myCertName = "my_certificate_to_pin"
        var remoteCertMatchesPinnedCert = false
        if let myCertPath = Bundle.main.path(forResource: myCertName, ofType: "der") {
            if let pinnedCertData = NSData(contentsOfFile: myCertPath) {
                // Compare certificate data
                let remoteCertData: NSData = SecCertificateCopyData(SecTrustGetCertificateAtIndex(trust, 0)!)
                if remoteCertData.isEqual(to: pinnedCertData as Data) {
                    print("*** CERTIFICATE DATA MATCHES")
                    remoteCertMatchesPinnedCert = true
                }
                else {
                    print("*** MISMATCH IN CERT DATA.... :(")
                }

            } else {
                print("*** Couldn't read pinning certificate data")
            }
        } else {
            print("*** Couldn't load pinning certificate!")
        }

        if remoteCertMatchesPinnedCert {
            print("*** TRUSTING CERTIFICATE")
            completionHandler(.useCredential, credential)
        } else {
            print("NOT TRUSTING CERTIFICATE")
            completionHandler(.rejectProtectionSpace, nil)
        }
    }
}

This class checks to see if you enabled certificate pinning. If you did, it completely ignores the normal certificate validation and does an exact comparison with the cert we include in the app. In this way, it only accepts your self-signed cert, and nothing else.

This solution requires that you put a "my_certificate_to_pin.der" file in your project, in your Resources folder. If you don't already have a Resources folder, just add one.

That certificate should be in DER format.

To create a self-signed certificate for your server, you would normally do something like this:

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout mycert.key -out mycert.cer

That generates two files -- a mycert.key private key file, and a mycert.cer -- the certificate itself. These are both in the X509 format. For iOS, you will need the cert in DER format, so do this:

openssl x509 -outform der -in mycert.cer -out my_certificate_to_pin.der

That generates the file you need on iOS.