When running the sample code after changing to my FB creds I get an authentication error.
"An SSL error has occurred and a secure connection to the server cannot be made"
This issue exists on GitHub page for Xamarin.Auth. https://github.com/xamarin/Xamarin.Auth/issues/95
The solution there was to make the following changes to the info.plist
NSAppTransportSecurity
NSExceptionDomains
facebook.com
NSIncludesSubdomains
NSThirdPartyExceptionRequiresForwardSecrecy
fbcdn.net
NSIncludesSubdomains
NSThirdPartyExceptionRequiresForwardSecrecy
akamaihd.net
NSIncludesSubdomains
NSThirdPartyExceptionRequiresForwardSecrecy
Now I get
Given URL is not allowed by the application configuration.
One or more of the given URLs is not allowed by the App's settings. It must match the website URL or Canvas URL, or the domain must be a subdomain or one of the App's domains.