Web Authentication Working Draft rev 7 (WD-07) is officially published here: https://www.w3.org/TR/2017/WD-webauthn-20171205/
NOTE: the latest official WebAuthn spec release is always available here: https://www.w3.org/TR/webauthn/ (so this presently yields WD-07)
Please also note that this spec is a _Working DRAFT_ and will change, possibly in “breaking” ways.