This is a Xamarin sample application that demonstrates certificate public key pinning.
See this OWASP page for reference.
This seems like a straightforward topic, but I struggled to find any working examples -- especially for Xamarin apps. I cobbled together bits from past experience, OWASP, this developer blog post, and Google to build a sample app using Xamarin that would show a pass and fail example of cert pinning in action on Android and iOS.
I've bundled a Lookup.PublicKeys app to help you lookup the public key for a site you're interested in.
I hope this sample helps someone else out.
I'm not a security pro, so if you find holes in my sample implementation, please let me know, open an issue, submit a PR, or whatever is easiest.