Row Level Security: DAX Filtering other than username()

I'm facing exact same issue and I suspect there are many others in the same boat.  It is not uncommon that 'user principal name' is not part of a user's record in a given database.  User's first and last name and user id are more common.  Also, the Username() function should be consistent in its behaviour across PowerBI platforms.   Is  there a RLS workaround for  data that holds only user's name but not email address ?  Solution that calls for setting up a relathiship hard-coding user to a targeted information will not work for my environment (as any users can submit any forms.  my RLS implementation just want to set a limited view for each user such that he can only see his own list of forms he submitted when he logs in to this report in Power BI Service).  Any help will be greatly appreciated. 

Thanks.

Pat