diff --git a/SDWebImage/Core/SDWebImageDownloaderOperation.m b/SDWebImage/Core/SDWebImageDownloaderOperation.m
index a2395c5c..446c36db 100644
--- a/SDWebImage/Core/SDWebImageDownloaderOperation.m
+++ b/SDWebImage/Core/SDWebImageDownloaderOperation.m
@@ -565,7 +565,9 @@ didReceiveResponse:(NSURLResponse *)response
                 credential = self.credential;
                 disposition = NSURLSessionAuthChallengeUseCredential;
             } else {
-                disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
+                // Web Server like Nginx can set `ssl_verify_client` to optional but not always on
+                // We'd better use default handling here
+                disposition = NSURLSessionAuthChallengePerformDefaultHandling;
             }
         } else {
             disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;