This is a relatively complete example of certificate pinning in Xamarin.Forms 4.0. For now it only sends a request to google.com and checks its certificate. On Android this requires some more work, but it's doable. You can send request using Refit or .NET.

For practice, you could refactor the code to connect to the included Azure Functions API project. To check its certificate, use:

openssl s_client -connect {YOUR DOMAIN}:443 | openssl x509 -pubkey -noout

To write it to a file, use:

echo -n | openssl s_client -connect google.com:443 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > {YOUR_FILENAME}.cert

https://thomasbandt.com/certificate-and-public-key-pinning-with-xamarin https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/Pinning_Cheat_Sheet.md https://docs.microsoft.com/en-us/xamarin/android/app-fundamentals/http-stack?context=xamarin%2Fcross-platform

Android can still have some name resolution failure issues. I wasn't able to resolve this.