Implement 'SDWebImageDownloaderAllowInvalidSSLCertificates' option.

Author: Pavel Osipov

SDWebImage/SDWebImageDownloaderOperation.m

@@ -396,8 +396,13 @@ - (BOOL)connectionShouldUseCredentialStorage:(NSURLConnection __unused *)connect
 
 - (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge{
     if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
-        NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
-        [[challenge sender] useCredential:credential forAuthenticationChallenge:challenge];
+        if (!(self.options & SDWebImageDownloaderAllowInvalidSSLCertificates) &&
+            [challenge.sender respondsToSelector:@selector(performDefaultHandlingForAuthenticationChallenge:)]) {
+            [challenge.sender performDefaultHandlingForAuthenticationChallenge:challenge];
+        } else {
+            NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
+            [[challenge sender] useCredential:credential forAuthenticationChallenge:challenge];
+        }
     } else {
         if ([challenge previousFailureCount] == 0) {
             if (self.credential) {