ok found it.
you can use the getUserPrincipal() method on the PortletRequest object.
If you are wondering where is the PortletRequest object, the "rRequest" object in protected void doView(RenderRequest rRequest, RenderResponse rResponse) is the PortletRequest object.
To get the actual user name you could use:
RenderRequest.getRemoteUser() will provide you with the string representation of the user. I recommend consulting the API JDoc for more info.