Alamofire无法获得用于客户端认证的NSURLAuthenticationMethodClientCertificate

Question

我使用Alamofire（4.7.3），Xcode 10（Swift4.2）。我使用这些代码进行相互认证

manager.delegate.sessionDidReceiveChallenge = { (session,challenge) in
    if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
            // it's ok
    }
    else if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodClientCertificate {
           // can't receive NSURLAuthenticationMethodClientCertificate
    }
)