Detect webauthn browser support

[phavekes]

This issue is imported from pivotal - Originaly created at Apr 29, 2021 by Peter Havekes

Detect if the browser supports webauthn before attempting authentication or registration. This can be done in javascript:

 if (typeof(PublicKeyCredential) == "undefined") {
   // Show a webpage informing the user about the unsupported browser,
   // and a button return the user to sa-gateway with a saml-error response
 }