WKWebView

Hello, I am implementing signature for an iOs application, I am showing with WKWebView.

but I don't know how to hide or close this WKWebView when the user has finished signing. used WKWebView delegates, but when you go from the signature view to the "Thank you" view, not  call none this delegates 

How can I know when the user has signed and can close the webView.?

  func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {