This should be possible via:
``` #substdef "/MYENVSECRET/$env(AUTH_EPHEMERAL_SECRET)/" modparam("auth_ephemeral", "secret", "MYENVSECRET") ``` There is another alternative to use command line parameters to set defined values or substdef rules, see `kamailio -h`.
I am going to close this one, having alternatives for it. If one wants to implement direct evaluation in modparams, then just do a pull request.