Hello Christian,
Shailaja's answer is correct for using it in commands.
Should you need it in user inputs - I am copying from another thread I responded to something similiar:
https://communities.netapp.com/message/95055#95055
In 2.0, if you'd go and define a user input called "$_WFAUser" you'd be able to get that value (Of the user currently logged in to WFA).
It would be a read only input (ie shown on the screen in preview) with a pre-defined tooltip.
You can use it in queries to correlate the logged in user with information from additional tables (Either native ones from the DFM cache
or with proprietary info from the user-specific playground DB).

While admittedly it can use a little more polish - I believe this is very usable and will offer a viable solution to most use cases.
Hope you might find that useful.
Thanks,
Yaron