USerprinciple Name

Hi Experts

I am using the following dax to restrict access to data in PBIX based on Country and Stores in the Country . But when i test the DAX in Managed Role it returns back nothing 

VAR _USERPRINCIPLENAME = "[country_dim.country_name];[bu_code]"

VAR SeparatorPosition = SEARCH(";",_USERPRINCIPLENAME)

VAR Country = LEFT(_USERPRINCIPLENAME, SeparatorPosition - 1)

RETURN

CONTAINSSTRING(Country, CONCATENATE("(", CONCATENATE([country_dim.country_name],")")))

Should tell me who is logged in???