Using DSN Connection and knowing windows username

i am using windows server 2012 and connecting from Access FE to Postgresql using DSN connection. 

When i am using "select current_user;" in postgresql i have always user "postgres" because it is my default user for database. 

How to know in postgresql which specific windows user is using database? 

How to solve this? 

I tried to use method from here:

but this is only to avoid inputing password by specific windows server user. 

(and this is not working also).

Please help,

Best,

Jacek