Restrict access to Element API endpoint I'd like to Restrict access to Element API endpoint by the current user's group. 

Is this possible Using Craft 2?
Yes it is you can see here how to check permissions 

You can get the current user with 

$currentUser = craft()-&gt;userSession-getUser();


Then you can check the same conditions like in the example link. If the conditions are false you can return an empty array instead of your endpoints 

if(!$currentUser-&gt;isInGroup('groupHandle')) {
    return [];
} 


Please make sure to check if the current user is not null