Getting the user who completed the user task

Hi camunda community!
let me say the exact thing i blocked with
i have process with some user tasks in it
and i call submit rest api endpoint and send form data to submit for these tasks and complete them
in the process start i do the same and send a form and start the process, but i have access to the user who started the process in initiator section and i set a process variable for it
now i want something exact same and the authenticated user which completed the task and set a variable for it, any script that do this for me? as a listener before or end of it?
sending that as a form data field is not an option for preventing some dependencies and also there is a group of users who can do it

Assuming you have access to the user context during the submit, the simplest way to accomplish a trace of who completed which task, using the mechanisms that already exist, would be to first claim the task for the user, then complete it. Camunda keeps track of task assignments, which can be used later if needed.