Add a new field ProbeResistanceAuthExternal that allows probe_resistance
to work without auth_credentials configured in forwardproxy itself.
This enables setups where authentication is handled externally (e.g. via
Caddy's forward_auth directive placed before forward_proxy in the route
order).
- New field: ProbeResistanceAuthExternal (bool)
- Provision() now skips the probe_resistance requires authentication
check when this flag is set
- Mutually exclusive with auth_credentials
- Caddyfile subdirective: probe_resistance_auth_external