This host exists only to hold a single permanent Google OAuth
redirect_uri. Google matches redirect URIs exactly and offers
no wildcards, so per-branch preview deployments — whose hostnames are not
known ahead of time — can never register their own. They point Google here
instead, and /api/callback/google forwards each callback on to
the preview deployment that started the sign-in.
There is nothing to use at this path. See apps/preview-auth in atlas-myco.