How to Connect localhost (with invalid certificate) using Alamofire?

Swift 3

In my case when I use swagger client library, I changed my code to test the local server like this:

 open func createSessionManager() -> Alamofire.SessionManager {
    let configuration = URLSessionConfiguration.default
    configuration.httpAdditionalHeaders = buildHeaders()

    let serverTrustPolicies: [String: ServerTrustPolicy] = ["localhost": .disableEvaluation]

    return Alamofire.SessionManager(configuration: configuration, serverTrustPolicyManager: ServerTrustPolicyManager(policies: serverTrustPolicies))
}

Swift 3 version of @cnoon's code

    manager.delegate.sessionDidReceiveChallenge = { session, challenge in
        var disposition: URLSession.AuthChallengeDisposition = .performDefaultHandling
        var credential: URLCredential?

        if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust, let trust = challenge.protectionSpace.serverTrust {
            disposition = URLSession.AuthChallengeDisposition.useCredential
            credential = URLCredential(trust: trust)
        } else {
            if challenge.previousFailureCount > 0 {
                disposition = .cancelAuthenticationChallenge
            } else {
                credential = self.manager.session.configuration.urlCredentialStorage?.defaultCredential(for: challenge.protectionSpace)

                if credential != nil {
                    disposition = .useCredential
                }
            }
        }

        return (disposition, credential)
    }

You can easily override the default challenge behavior in Alamofire using the SessionDelegate override closures. Here is an example of how you can allow Alamofire to accept invalid certificates:

IMPORTANT: Please do not use this in any production code. Security is VERY important and this implementation completely disregards the security mechanisms in Alamofire. Use at your own risk!

let manager = Alamofire.Manager.sharedInstance

manager.delegate.sessionDidReceiveChallenge = { session, challenge in
    var disposition: NSURLSessionAuthChallengeDisposition = .PerformDefaultHandling
    var credential: NSURLCredential?

    if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
        disposition = NSURLSessionAuthChallengeDisposition.UseCredential
        credential = NSURLCredential(forTrust: challenge.protectionSpace.serverTrust)
    } else {
        if challenge.previousFailureCount > 0 {
            disposition = .CancelAuthenticationChallenge
        } else {
            credential = manager.session.configuration.URLCredentialStorage?.defaultCredentialForProtectionSpace(challenge.protectionSpace)

            if credential != nil {
                disposition = .UseCredential
            }
        }
    }

    return (disposition, credential)
}

We (the Alamofire TC) are going to implement TLS pinning and several other features related to security in the Alamofire 1.3.0 release.

---

UPDATE

The Alamofire 1.3.0 release is out and adds MUCH better support for customizing server trust authentication challenges. For further info, please check out the Security section of the README.