how to filter data based on logged user

Hi,

I would like to be able to filter data based on the logged user.

I would like to create one mashapp with sensible information like selling data. But I would like that specific user could see only his selling data, not all the data of the company.

I was thinking to a DataBase table with a column containing the username, close to the selling data. 

I know I can create 2 different mashapp that use a unique global datafeed and set up filter inside the mashapp. And then give specific share grant to different users.

But I wonder if it's possible to add a filter at the level of datafeed. I mean, Building the datafeed, I would like to add something like a dinamic parameter "$USER" that can be used in the datafeed to filter information.

In this way automatically, in the mashapp the system could filter data based on the logged user.

Thanks

Dario