Expected signature:

virtual AuthRequiredResponse OnAuthRequired(
      URLRequest* request,
      const AuthChallengeInfo& auth_info,
      const AuthCallback& callback,
      AuthCredentials* credentials) = 0;

Actual signature:

virtual void OnAuthRequired(WebState* source,
                            NSURLProtectionSpace* protection_space,
                            NSURLCredential* proposed_credential,
                            const AuthCallback& callback) = 0;