Add webtests mirroring the v1 coverage for the v2 auth surface:
register (incl. registration-disabled 404), password reset request +
reset, email confirm, link-share auth (password matrix), the OAuth token
flow in both JSON and form-urlencoded encodings, oauth/authorize, the
token-test/check endpoints (200, not 418), /routes and link-share token
renewal (incl. user-token rejection).
Also make the link-share auth body optional so a passwordless share
authenticates with no request body, matching v1.
kolaente