routing_valhalla_provider (fossgis, trek or custom) sits beside the routing
URLs under Admin, Default user settings, admin only and locked on a managed
install. Without a choice an own Valhalla is custom, an own OSRM alone asks
no Valhalla, and otherwise the TREK services answer.
The planner asks them through the same-origin relay, so no connect-src
changes. A relay that answers 401 (a shared page without a sign-in), 403,
413, 429 or 5xx sends the question to FOSSGIS without a word and is left
alone for ten minutes. A long line to describe goes as a polyline.
Maurice