title: ASWebAuthenticationSession on iOS 13
body: <p>I installed iOS 13, the authentication via Safari no longer works.
  I have the same configuration on iOS 12 except <code>self.authSessionAS.presentationContextProvider = self;</code></p>
  
  <pre class="lang-c prettyprint-override"><code>self.authSessionAS = [[ASWebAuthenticationSession alloc]initWithURL:[[NSURL alloc] initWithString:self.authUrl] callbackURLScheme:@"app://" completionHandler:^(NSURL * _Nullable callbackURL, NSError * _Nullable error) {
      if(callbackURL)
      {
          self.resultStream(callbackURL.absoluteString);
      }else
      {
          self.resultStream(@"");
      }
      self.resultStream = NULL;
  }];
  
  self.authSessionAS.presentationContextProvider = self;
  [self.authSessionAS start];
  </code></pre>