Webauthn module is deprecated

[thatoddmailbox]

Apparently our webauthn module is deprecated. Building the server gives me go: module github.com/duo-labs/webauthn is deprecated: use github.com/go-webauthn/webauthn instead.

I don't think the webauthn stuff is actually working yet so this probably doesn't matter too much? But we should probably still fix it at some point.