Signalling build completion without token?

If a client calls the /unattended/built URL directly on the Sat then no token is required, presumably client IP is used. However, from the Proxy a token is required to avoid Net::HTTPMethodNotAllowed response.

My build process doesn’t enable me to inject the token into the image, so I’m trying to figure out a method to achieve clients signalling their build is complete through the proxy. I’d hoped that X-Forwarder-For would be supported, but that doesn’t appear to be the case?

Are there any other ways I can achieve this?