Authentication ACS <-> CPE v1.2

I haven’t yet found how to authenticate both ways (ACS -> CPE and CPE -> ACS) in v1.2 of GenieACS. And it doesn’t help that http://docs.genieacs.com/en/latest/cpe-authentication.html isn’t written.

In the release at GitHub, it is stated that

“the connection request authentication behavior can now be customized using an ‘expression’.”

Which expression?

Thank you

See my answer here: Incorrect connection request credentials (v1.2)