Auth on scripts for clustered environments

Enonic version: 7.8.5
OS: Linux


We have an important system service, triggered on the frontend, that should work doing requests on live and preview modes, and recently upgraded our servers from XP 7.4 to 7.8.
One of the issues we’re facing now is due basic auth being disabled on default (Auth header is not working anymore). We went for the cookies approach, which seems much faster to develop and deploy than creating another idprovider, and it worked neatly on all test environments, except the one that’s clustered (as production is).
Are the cookies bound to a cluster-node? Is there an easier way of getting the service authorized to do requests in preview than creating another idprovider (which could support basic auth)?