How to check origin URL when loading a web archive inside WKWebView

Introduction

We load a saved web archive (NSData) into a WKWebView instance using following method:

[self.webView loadData: archive
                  MIMEType:@"application/x-webarchive"
     characterEncodingName:@""
                   baseURL:baseURL];

We also have some custom scripts injected safely into the web view using following snippet

WKUserScript *userScript = [[WKUserScript alloc] initWithSource:<jsfilename> injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:onMainFrame];

[webview.configuration.userContentController addUserScript:userScript];

Things work fine till here.

Observation

When I get the call from Javascript Layer to the native iOS Layer via:

-[CustomWebViewController userContentController:didReceiveScriptMessage:]

the value message.frameInfo.request.URL.absoluteString is "about:blank"

Question

Is there any way to get the original baseURL back here?

Alternatives Considered:

Store the baseUrl in an instance variable and use it here but since we are using this url to determine if the request is coming from valid domains, having a url from this method will be most credible.

We are looking a way to piggyback this info (baseURL domain) to our web archive at the time of loading it in webView and extract that from the -[CustomWebViewController userContentController:didReceiveScriptMessage:] method

Any help will be much appreciated.