What command logstash uses to read log files?

We have logfiles that has permissions 600 (only owner can read and not readable by group or everyone). The permission "600" is set by automated scripts and cannot be changed in our setup. Logstash forwarder can forward logs if we run it as root but not with regular unix user (say, loguser).

I applied sudo for "cat" and "tail" command for the user "loguser" but that didn't work. Does anyone know how logstash forwarder reads log files? Does it reads log files using a specific command? If yes, adding sudo for that command for "loguser" would be able to read logs with "600" permission? Thanks so much for help.