iOS Https证书验证问题全解

在调用Https地址请求数据时，我们会遇到证书验证的问题。
关于证书调用的方法。主要有两个代理
这两个方法是不同的，一个是session负责处理，一个是task负责处理，处理的方式一样，一般我们会用session来处理。


Requests credentials from the delegate in response to a session-level authentication request from the remote server.
从委托请求凭据，以响应来自远程服务器的会话级身份验证请求。
optional func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void)

When a remote server asks for client certificates or Windows NT LAN Manager (NTLM) authentication, to allow your app to provide appropriate credentials

When a session first establishes a connection to a remote server that uses SSL or TLS, to allow your app to verify the server’s certificate chain
If you do not implement this method, the session calls its delegate’s urlSession(_:task:didReceive:completionHandler:) method instead.

翻译：

这种方法在两种情况下调用:
当远程服务器请求客户端证书或Windows NT LAN Manager (NTLM)身份验证时，允许您的应用程序提供适当的凭据
当会话首次建立到使用SSL或TLS的远程服务器的连接时，允许您的应用程序验证服务器的证书链
如果不实现此方法，则会话将调用其委托的urlSession(_:task:didReceive:completionHandler:)方法。

当sesion的代理方法未实现时，会执行下面的这种方式，如果两种方法都未实现的时候会怎么处理呢？我们下面会说到。

Requests credentials from the delegate in response to an authentication request from the 
remote server.
从委托请求凭据以响应来自远程服务器的身份验证请求。
optional func urlSession(_ session: URLSession, task: URLSessionTask, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void)

This method handles task-level authentication challenges. The URLSessionDelegate protocol also provides a session-level authentication delegate method. The method called depends on the type of authentication challenge:
For session-level challenges—NSURLAuthenticationMethodNTLM, NSURLAuthenticationMethodNegotiate, NSURLAuthenticationMethodClientCertificate, or NSURLAuthenticationMethodServerTrust—the NSURLSession object calls the session delegate’s urlSession(_:didReceive:completionHandler:) method. If your app does not provide a session delegate method, the NSURLSession object calls the task delegate’s urlSession(_:task:didReceive:completionHandler:) method to handle the challenge.
For non-session-level challenges (all others), the URLSession object calls the session delegate’s urlSession(_:task:didReceive:completionHandler:) method to handle the challenge. If your app provides a session delegate and you need to handle authentication, then you must either handle the authentication at the task level or provide a task-level handler that calls the per-session handler explicitly. The session delegate’s urlSession(_:didReceive:completionHandler:) method is not called for non-session-level challenges.

翻译：

此方法处理任务级身份验证挑战。URLSessionDelegate协议还提供了一个任务级的身份验证委托方法。所调用的方法取决于认证挑战的类型:
对于会话级别的挑战——nsurlauthenticationmethodntlm、NSURLAuthenticationMethodNegotiate、NSURLAuthenticationMethodClientCertificate或nsurlauthenticationmethodservertrust——NSURLSession对象调用会话委托的urlSession(_:didReceive:completionHandler:)方法。如果你的应用程序没有提供一个会话委托方法，NSURLSession对象会调用任务委托的urlSession(_:task:didReceive:completionHandler:)方法来处理这个挑战。
对于非会话级别的挑战(所有其他挑战)，URLSession对象调用会话委托的URLSession (_:task:didReceive:completionHandler:)方法来处理该挑战。如果您的应用程序提供了一个会话委托，而您需要处理身份验证，那么您必须在任务级处理身份验证，或者提供一个显式调用每个会话处理程序的任务级处理程序。对于非会话级挑战，不会调用会话委托的urlSession(_:didReceive:completionHandler:)方法。

这两个代理方法的总结就是，如果是session级别的验证，那么可以使用任一一种方法解决。
如果是非会话级别的验证（on-session-level challenges (all others)），那么session级别不能替代task级别。

不同的请求验证方式

NSURLAuthenticationMethodClientCertificate
此保护空间使用客户端证书身份验证。
NSURLAuthenticationMethodNegotiate
协商在这个保护空间中使用Kerberos还是NTLM身份验证。
NSURLAuthenticationMethodNTLM
对这个保护空间使用NTLM身份验证。
NSURLAuthenticationMethodServerTrust
为这个保护空间执行服务器信任身份验证(证书验证)。

在处理会话的时候，将分为三个部分

验证服务器证书 NSURLAuthenticationMethodServerTrust
服务器验证本地 NSURLAuthenticationMethodClientCertificate
其他 NSURLAuthenticationMethodNTLM,NSURLAuthenticationMethodNegotiate

一般我们会用到两种，一种是我们验证服务器，一种是服务器验证客户端。

NSURLAuthenticationMethodServerTrust

如果我们验证服务器的话，可以有两种方式

直接验证通过
使用代码和证书验证

  //不做任何验证，直接信任服务器
    static private func trustServer(challenge: URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?) {
        let disposition = URLSession.AuthChallengeDisposition.useCredential
        let credential = URLCredential.init(trust: challenge.protectionSpace.serverTrust!)
        return (disposition, credential)
        
    }

    //验证服务器证书
    static private func trustServerWithCer(challenge: URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?) {
        
        var disposition: URLSession.AuthChallengeDisposition = .performDefaultHandling
        var credential: URLCredential?
        
        //获取服务器发送过来的证书
        let serverTrust:SecTrust = challenge.protectionSpace.serverTrust!
        let certificate = SecTrustGetCertificateAtIndex(serverTrust, 0)!
        let remoteCertificateData = CFBridgingRetain(SecCertificateCopyData(certificate))!
         //加载本地CA证书
        let cerPath = Bundle.main.path(forResource: "你本地的cer证书文件名", ofType: "cer")!
        let cerUrl = URL(fileURLWithPath:cerPath)
        let localCertificateData = try! Data(contentsOf: cerUrl)
        if (remoteCertificateData.isEqual(localCertificateData) == true) {            
            //服务器证书验证通过
            disposition = URLSession.AuthChallengeDisposition.useCredential
            credential = URLCredential(trust: serverTrust)            
        } else {
            //服务器证书验证失败
            disposition = URLSession.AuthChallengeDisposition.cancelAuthenticationChallenge
        }
        return (disposition, credential)
    }

NSURLAuthenticationMethodClientCertificate

 //发送客户端证书交由服务器验证
    static private func sendClientCer() -> (URLSession.AuthChallengeDisposition, URLCredential?) {
        
        let disposition = URLSession.AuthChallengeDisposition.useCredential
        var credential: URLCredential?
        
        //获取项目中P12证书文件的路径
        let path: String = Bundle.main.path(forResource: "你本地的p12证书文件名", ofType: "p12")!
        let PKCS12Data = NSData(contentsOfFile:path)!
        let key : NSString = kSecImportExportPassphrase as NSString
        let options : NSDictionary = [key : "p12证书的密码"] //客户端证书密码
        
        var items: CFArray?
        let error = SecPKCS12Import(PKCS12Data, options, &items)
        
        if error == errSecSuccess {
            
            let itemArr = items! as Array
            let item = itemArr.first!
            
            let identityPointer = item["identity"];
            let secIdentityRef = identityPointer as! SecIdentity
            
            let chainPointer = item["chain"]
            let chainRef = chainPointer as? [Any]
            
            credential = URLCredential.init(identity: secIdentityRef, certificates: chainRef, persistence: URLCredential.Persistence.forSession)
            
        }
        
        return (disposition, credential)
        
    }