In a discussion at
https://www.postgresql.org/message-id/55D51B54.4050902@joh.to we talked about adding RADIUS fallback servers. It never got to the point of it being done.
PFA a patch that implements this.
It supports multiple RADIUS servers. For all other parameters (secret, port, identifier) one can specify either the exact same number of entries, in which case each server gets it's own, or exactly one entry in which case that entry will apply to all servers. (Or zero entries for everything except secret, which will make it the default).
Each server is tried in order. If it responds positive, auth is OK. If it responds negative, auth is rejected. If it does not respond at all, we move on to the next one.
I'm wondering if in doing this we should also make the RADIUS timeout a configurable as HBA option, since it might become more important now?
