Swift iOS Client Certificate Authentication

Question

The web service I want to consume requires a client certificate. How can I send my certificate to it?

To further elaborate I don't understand how to create the SecIdentityRef.

In my NSURLConnection didReceiveAuthenticationChallenge I've got this conditional after ServerTrust:

else if challenge?.protectionSpace.authenticationMethod == NSURLAuthenticationMethodClientCertificate
    {
        var secIdent : SecIdentityRef = ?????????
        var certCred = NSURLCredential(identity: secIdent, certificates: [getClientCertificate()], persistence: NSURLCredentialPersistence.Permanent)
        challenge?.sender.useCredential(certCred, forAuthenticationChallenge: challenge!)
    }

The getClientCertificate method:

func getClientCertificate() -> SecCertificateRef
{
    let mainBundle : NSBundle = NSBundle.mainBundle()
    var mainBund = mainBundle.pathForResource("iosClientCert", ofType: "cer") //exported the cert in der format.
    var key : NSData = NSData(contentsOfFile: mainBund!)!
    var turnToCert : SecCertificateRef = SecCertificateCreateWithData(kCFAllocatorDefault, key).takeRetainedValue()

    return turnToCert;
}

Answer 1

Technically, when someone I know needed the implementation in Swift, he used the following Objective-C implementation in order to get the NSURLCredential object to the connection; based on the private key and X509 Certificate pair contained in a PKCS12 keystore.

Sorry, I don't have access to the source with the Swift solution. All I know is that the NSURLCredential was returned to Swift, and used directly in the http url connection there. It's similar to this one, though.

I'm not an iOS dev so I won't be able to help you out with the "bridging to Swift" part.

- (void)getMessageWithURL:(NSString *)url {

    NSURL *URL = [NSURL URLWithString:url];

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:URL];
    [request setHTTPMethod:@"GET"];
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    [connection self];
}

- (void)postMessageWithURL:(NSString *)url withContent:(NSString *)content {

    NSData *postData = [content dataUsingEncoding:NSUTF8StringEncoding];
    NSString *postLength = [NSString stringWithFormat:@"%d", [postData length]];

    NSURL *myURL = [NSURL URLWithString:url];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:myURL cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:60];

    [request setHTTPMethod:@"POST"];
    [request setValue:postLength forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    [request setHTTPBody:postData];

    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    [connection self];

}

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

- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
    NSLog(@"didReceiveAuthenticationChallenge");
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    responseData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"Unable to fetch data");
    NSLog(@"%@", error);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"Succeeded! Received %lu bytes of data", (unsigned long)[responseData
            length]);

    NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
    NSLog(@"%@", responseString);

    [bridge callHandler:handlerName data:responseString];

}

- (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {

    /*
    Reading the certificate and creating the identity
    */
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = paths[0]; // Get documents directory

    NSData *p12data = [CertificateManager getP12Data]; //returns essentially a byte array containing a valid PKCS12 certificate

    if (!p12data) {
      return;
      NSAssert(p12data, @"Couldn't load p12 file...");
    }

    CFStringRef password = CFSTR("password");

    const void *keys[] = {kSecImportExportPassphrase};
    const void *values[] = {password};
    CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
    CFArrayRef p12Items;

    OSStatus result = SecPKCS12Import((__bridge CFDataRef) p12data, optionsDictionary, &p12Items);

    if (result == noErr) {
        CFDictionaryRef identityDict = CFArrayGetValueAtIndex(p12Items, 0);
        SecIdentityRef identityApp = (SecIdentityRef) CFDictionaryGetValue(identityDict, kSecImportItemIdentity);

        SecCertificateRef certRef;
        SecIdentityCopyCertificate(identityApp, &certRef);

        SecCertificateRef certArray[1] = {certRef};
        CFArrayRef myCerts = CFArrayCreate(NULL, (void *) certArray, 1, NULL);
        CFRelease(certRef);

        NSURLCredential *credential = [NSURLCredential credentialWithIdentity:identityApp certificates:nil persistence:NSURLCredentialPersistenceNone];
        CFRelease(myCerts);

        [[challenge sender] useCredential:credential forAuthenticationChallenge:challenge];
    }
    else {
        // Certificate is invalid or password is invalid given the certificate
        NSLog(@"Invalid certificate or password");
        NSError *error = [NSError errorWithDomain:NSOSStatusErrorDomain code:result userInfo:nil];
        return;
    }
}

EDIT: Har har, very funny, downvoting me twice when you yourself didn't bother while the bounty was up. *grumble *

Anyways, to use the following above, you just need to access it from Swift.

func connection(connection: NSURLConnection, willSendRequestForAuthenticationChallenge challenge: NSURLAuthenticationChallenge) {
    if let p12Data = UserManager.currentP12,
       let credential = CertificateManager.getCredentialsForP12(p12Data) as? NSURLCredential {
            challenge.sender.useCredential(credential, forAuthenticationChallenge: challenge)
    } else {
        UIApplication.sharedApplication().networkActivityIndicatorVisible = false
    }   
}

That uses this.

+ (id)getCredentialsForP12:(NSData *)p12 {
    NSData* p12data = p12;
    const void *keys[] = {kSecImportExportPassphrase};
    const void *values[] = {CFSTR("thePassword")};
    CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
    CFArrayRef p12Items;
    OSStatus result = SecPKCS12Import((__bridge CFDataRef) p12data, optionsDictionary, &p12Items);
    if (result == noErr) {
        CFDictionaryRef identityDict = CFArrayGetValueAtIndex(p12Items, 0);
        SecIdentityRef identityApp = (SecIdentityRef) CFDictionaryGetValue(identityDict, kSecImportItemIdentity);
        SecCertificateRef certRef;
        SecIdentityCopyCertificate(identityApp, &certRef);
        SecCertificateRef certArray[1] = {certRef};
        CFArrayRef myCerts = CFArrayCreate(NULL, (void *) certArray, 1, NULL);
        CFRelease(certRef);

        NSURLCredential *credential = [NSURLCredential credentialWithIdentity:identityApp certificates:nil persistence:NSURLCredentialPersistenceNone];
        CFRelease(myCerts);
        return credential;

    }
    else {
        // Certificate is invalid or password is invalid given the certificate
        NSLog(@"Invalid certificate or password");

        UIAlertView* av = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Invalid cert or pass" delegate:nil cancelButtonTitle:@"ok" otherButtonTitles: nil];
        [av show];
        NSError *error = [NSError errorWithDomain:NSOSStatusErrorDomain code:result userInfo:nil];
        return nil;
    }

EDIT: A swift version of the above is here, although it was messy enough that we rather just didn't use it.

            var p12items : Unmanaged<CFArrayRef>?

            let index: CFIndex = 1
            let password: CFString = "password"
            let key = kSecImportExportPassphrase.takeRetainedValue() as String
            var values = [unsafeAddressOf(password)]
            var keys = [unsafeAddressOf(key)]

            var keyCallbacks = kCFTypeDictionaryKeyCallBacks
            var valueCallbacks = kCFTypeDictionaryValueCallBacks

            let length: CFIndex = p12Data.length
            let p12CfData: CFData = CFDataCreate(kCFAllocatorDefault, UnsafePointer<UInt8>(p12Data.bytes), length)

            let options = CFDictionaryCreate(kCFAllocatorDefault, &keys, &values, index, &keyCallbacks, &valueCallbacks)
            let result = SecPKCS12Import(p12CfData, options, &p12items)

            if result == noErr {

                let idIndex: CFIndex = 0
                var items = p12items?.takeRetainedValue()
                var identityDict = CFArrayGetValueAtIndex(items!, idIndex) 

                var key = kSecImportItemIdentity.takeRetainedValue() as String
                var keyAddress = unsafeAddressOf(key)
                var identityApp: SecIdentityRef = CFDictionaryGetValue(identityDict, keyAddress) 
                var certRef : Unmanaged<SecCertificateRef>?
                SecIdentityCopyCertificate(identityApp, &certRef)

                var cert: SecCertificateRef = certRef!.takeRetainedValue()
                var certArray = [unsafeAddressOf(cert)]
                var arrayCallback = kCFTypeArrayCallBacks
                var myCerts: CFArrayRef = CFArrayCreate(kCFAllocatorDefault, &certArray, index, &arrayCallback);

                let credential: NSURLCredential = NSURLCredential(identity: identityApp, certificates: [AnyObject](), persistence: NSURLCredentialPersistence.None)