Hello,
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As you said “open a website in my app to make the user log in to a specific page”, I recommend you to use Xamarin.Essentials: Web Authenticator,this often means enabling your users to sign in their existing Microsoft, Facebook, Google, and now Apple Sign In accounts.
If you want to get the return value of web, invoking a JavaScript function in C # may be a good choice. It need to be handled in Javascript code on the web page side, this requires you know about Javascript. For more infor information, you can refer to
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/webview?tabs=windows#invoking-javascript
Best Regards,
Wenyan Zhang
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