Have you mentioned using SSL Pinning in your projects?

Yes, in some projects I have used SSL Pinning to enhance network security. SSL Pinning is a technique where the application stores a specific server certificate or public key and verifies it during the establishment of an HTTPS connection to prevent "man-in-the-middle" attacks.

In practice, this means that even if an attacker replaces the certificate, the application will not accept the connection because the certificate does not match the pinned one.

An example of using SSL Pinning in iOS with URLSession:

let session = URLSession(configuration: .default, delegate: self, delegateQueue: nil)

// Implementing the URLSessionDelegate
func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge,
                completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {
    if let serverTrust = challenge.protectionSpace.serverTrust,
       SecTrustEvaluateWithError(serverTrust, nil) {
        // Get the server's certificate
        let serverCertificate = SecTrustGetCertificateAtIndex(serverTrust, 0)
        // Compare with the locally stored certificate
        // If it matches, allow the connection
        // Otherwise, reject
    } else {
        completionHandler(.cancelAuthenticationChallenge, nil)
    }
}

Thus, SSL Pinning helps protect the application from certificate substitution and enhances data transmission security.