I do not know, but IIRC, PVE does send it via UDP so there is no authentication as far as I understand the connectionless approach there.
A simple workaround would be to use a kind of a proxy influxdb on the PVE itself that receives the stuff from PVE and forwards it via authenticated http to your "outside influxdb".
Hi!
Finally, I create a new influxdb database with no credentials and allowing only proxmox IP.