The best approach IMO is to provide an option to inject headers using an environment variable, than simply configure it externally

Yes, exactly.

Hi @<1575656665519230976:profile|SkinnyBat30> , do you mean you need to add custom headers to any call to the API server?

This would require a code-change, though (we welcome PRs 🙂 )

I'm looking at from clearml.backend_api.session.client import APIClient rigt now.

OK, thanks. I'll look into it. I might be able to handle the injections via some cloudflare rules.

I'm getting "Object of type "StrictSession" is not callable"

The underlying session object used by clearml does not allow providing custom headers at the moment, but it can be added quite easily (see here and here ).
Most calls from within the API can add custom headers, but it would be much easier to inject them at these points than to change the entire code base 🙂