Port oauth/token and oauth/authorize to /api/v2, delegating to the
shared oauth2server.ExchangeToken / Authorize cores.
The token endpoint accepts spec-compliant application/x-www-form-urlencoded
bodies (RFC 6749) in addition to JSON; a form-urlencoded format is
registered on the v2 API that binds into the same json-tagged request
struct. The response carries Cache-Control: no-store. The token endpoint
is public; authorize inherits the global JWT auth.