Accept self signed certificate in WKWebView

I am trying to load local resources in a WKWebView using HTTPS and a local web server. I've used Telegraph to implement the local web server. The local web server is using a self signed certificate. I understand that the implementation below of this WKNavigationDelegate method is necessary to accept a web server's self signed certificate. I've managed to get the WKWebView to load local resources on iOS 11 and above, but the method below is not called for the localhost on iOS 10 and I have seen this error in the Safari Web Inspector:

Failed to load resource: The certificate for this server is invalid. You might be connecting to a server that is pretending to be “localhost” which could put your confidential information at risk.

- (void)webViewDidReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential *_Nullable))completionHandler

{

    NSString *authenticationMethod = challenge.protectionSpace.authenticationMethod;

    if ([authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust])

    {

        NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];

        completionHandler(NSURLSessionAuthChallengeUseCredential, credential);

        return;

    }


    completionHandler(NSURLSessionAuthChallengePerformDefaultHandling, nil);
}

Is there a way to fix the error above and accept self signed certificates on iOS 10?