A public client identifies itself to the provider with a hosted
Client ID Metadata Document. Serve it unauthenticated and outside the
auth group, since the provider fetches it server-to-server, exposing the
deployment-derived client_id and redirect_uri alongside the Probo brand
name, homepage and logo.
Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>