如果您不愿意(或不能)使用私有api，可以使用一个名为ASIHTTPRequest的开源(BSD许可)库，该库提供了底层CFNetwork api的包装器。他们最近通过- setvalidatessecureccertificate: API引入了允许使用自签名或不受信任证书的HTTPS连接的功能。如果不想提取整个库，可以使用源代码作为自己实现相同功能的参考。

在iOS 9中，对于所有无效或自签名的证书，SSL连接将失败。这是iOS 9.0或更高版本、OS X 10.11及更高版本中新的应用程序传输安全特性的默认行为。

您可以在“信息”中覆盖此行为。通过在NSAppTransportSecurity字典中将NSAllowsArbitraryLoads设置为YES。但是，我建议仅为测试目的重写此设置。

有关信息，请参阅这里的应用程序传输技术说明。

To complement the accepted answer, for much better security, you could add your server certificate or your own root CA certificate to keychain( https://stackoverflow.com/a/9941559/1432048), however doing this alone won't make NSURLConnection authenticate your self-signed server automatically. You still need to add the below code to your NSURLConnection delegate, it's copied from Apple sample code AdvancedURLConnections, and you need to add two files(Credentials.h, Credentials.m) from apple sample code to your projects.

- (BOOL)connection:(NSURLConnection *)connection canAuthenticateAgainstProtectionSpace:(NSURLProtectionSpace *)protectionSpace {
return [protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust];
}

- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
//        if ([trustedHosts containsObject:challenge.protectionSpace.host])

    OSStatus                err;
    NSURLProtectionSpace *  protectionSpace;
    SecTrustRef             trust;
    SecTrustResultType      trustResult;
    BOOL                    trusted;

    protectionSpace = [challenge protectionSpace];
    assert(protectionSpace != nil);

    trust = [protectionSpace serverTrust];
    assert(trust != NULL);
    err = SecTrustEvaluate(trust, &trustResult);
    trusted = (err == noErr) && ((trustResult == kSecTrustResultProceed) || (trustResult == kSecTrustResultUnspecified));

    // If that fails, apply our certificates as anchors and see if that helps.
    //
    // It's perfectly acceptable to apply all of our certificates to the SecTrust
    // object, and let the SecTrust object sort out the mess.  Of course, this assumes
    // that the user trusts all certificates equally in all situations, which is implicit
    // in our user interface; you could provide a more sophisticated user interface
    // to allow the user to trust certain certificates for certain sites and so on).

    if ( ! trusted ) {
        err = SecTrustSetAnchorCertificates(trust, (CFArrayRef) [Credentials sharedCredentials].certificates);
        if (err == noErr) {
            err = SecTrustEvaluate(trust, &trustResult);
        }
        trusted = (err == noErr) && ((trustResult == kSecTrustResultProceed) || (trustResult == kSecTrustResultUnspecified));
    }
    if(trusted)
        [challenge.sender useCredential:[NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust] forAuthenticationChallenge:challenge];
}

[challenge.sender continueWithoutCredentialForAuthenticationChallenge:challenge];
}

理想情况下，iOS应用程序需要接受不受信任的证书时，应该只有两种情况。

场景A:您连接到使用自签名证书的测试环境。

场景B:您正在代理HTTPS流量使用MITM代理，如Burp Suite, Fiddler, OWASP ZAP等。代理将返回一个由自签名CA签名的证书，以便代理能够捕获HTTPS流量。

出于显而易见的原因，生产主机绝不应使用不受信任的证书。

如果你需要让iOS模拟器接受一个不受信任的证书用于测试目的，强烈建议你不要为了禁用NSURLConnection api提供的内置证书验证而更改应用程序逻辑。如果应用程序在没有删除此逻辑的情况下发布给公众，它将容易受到中间人攻击。

出于测试目的而接受不受信任证书的推荐方法是将签署证书的证书颁发机构(CA)证书导入您的iOS模拟器或iOS设备。我写了一篇快速的博客文章来演示如何在iOS模拟器中做到这一点:

使用ios模拟器接受不受信任的证书

与AFNetworking我已经成功地消费https webservice与以下代码，

NSString *aStrServerUrl = WS_URL;

// Initialize AFHTTPRequestOperationManager...
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
manager.responseSerializer = [AFJSONResponseSerializer serializer];

[manager.requestSerializer setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
manager.securityPolicy.allowInvalidCertificates = YES; 
[manager POST:aStrServerUrl parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject)
{
    successBlock(operation, responseObject);

} failure:^(AFHTTPRequestOperation *operation, NSError *error)
{
    errorBlock(operation, error);
}];

NSURLRequest有一个叫做setAllowsAnyHTTPSCertificate:forHost:的私有方法，它会做你想做的事情。你可以通过一个类别在NSURLRequest上定义allowsAnyHTTPSCertificateForHost:方法，并设置它为你想要覆盖的主机返回YES。