Copy To File Share - Username Question

I am very new to using Nintex (2013), however I have already created a couple "Notification" workflows using conditions and find it quite intuitive.

I am using a combination of the two solutions shown in the posts below to create a workflow that copies Major versions of documents to a file share for archive purposes.

https://community.nintex.com/t5/Nintex-for-SharePoint/Copy-a-Major-version-of-a-document/m-p/38764#M32050
https://community.nintex.com/t5/Nintex-for-SharePoint/Add-sufix-to-output-filename-when-using-quot-Copy-file-to-File/td-p/113099

For testing purposes, I used my credentials in the Username and Password fields, but I would like these fields to be variable based on the user that is updating the document in SharePoint.

I researched the help files and many posts on this forum, however I can not find any info on this.

Is there a way to use a reference to the current user (or Initiator) to use their credentials in these fields?
How is this normally handled?

Thank-you!