Good starting point:
Related demo site sponsored by Cisco that includes a bunch of existing libraries including Java that might be a starting point:
Welcome to webauthn.io! This site is designed by Duo Labs to test the new W3C Specification Web Authentication. WebAuthn is supported in the Chrome, Firefox, and Edge browsers to different degrees, but support for credential creation and assertion using a U2F Token, like those provided by Yubico and Feitian, is supported by all of them.
PS. no recommendation there… just adding a bit of colour for others new to the topic!