In the current version, it is not possible. There are plans to bring this functionality in the future. However you can add rules to form initialize to check logged in user details and decide whether to load the form or close it.

Thanks Sujeeth. 

With a rule in the initialize method, would we be hardcoding the usernames (or any other information) to compare with the user details of the logged in user? I just want to make sure I am clear on this work around until a robust solution is available from K2.

Regards,

Adnan

You don't need to hardcode. You can have a smartobject that stores the users who can access. If the logged in user details match the smartobject results, proceed further, else show message box

Thanks Sujeeth.

Adnan