Pass username as filter or parameter in query using DirectQuery to SQL?

I was hoping to find a way to pass it into SQL as a parameter, I looked at using M but I didn't see any options for passing usernames that way (rather I didn't see a username function for M).

Ideally, I would be able to do a SELECT Col1, Col2, Col3 FROM Table1 WHERE Table1.Username=username()

(from PBI of course) however, I don't see anyway to pass system variables/parameters into queries.

I wanted to filter them BEFORE they are loaded, so if my table had 1 million records, I would much rather return only the records that matched UserName() instead of the entire table.