Config file syntax: secrets from file in key=value

Hi!

I'd like to set up proxy authentication. This works fine, but I cannot get the passwords in to be read from file.

Specifically I have this passdb block.

passdb { driver = passwd-file mechanisms = plain scram-sha-256 default_fields = proxy=y host=dovecot-backend master=imapc-master-user proxy_mech=plain pass=

This sets the password to the string /run/secrets/dovecot.imapc-master-user/password. I'd like the password to be set to the content of said file.

Is it possible to get the password from a file or less desirable from the environment? Reading https://doc.dovecot.org/configuration_manual/config_file/ I assume it's not.

Cheers, Tobias Florek