Enable authentication on KPsul websocket.

- PermConsumerMixin allows checking permissions on connection to a
  consumer.
- KPsul consumer uses this mixin to check if connecting user has the
  permission `kfet.is_team`.

Fixes #67.

kfet/consumers.py

@@ -17,5 +17,25 @@ class DjangoJsonWebsocketConsumer(JsonWebsocketConsumer):
         return json.dumps(content, cls=DjangoJSONEncoder)
 
 
-class KPsul(DjangoJsonWebsocketConsumer):
+class PermConsumerMixin(object):
+    """Add support to check permissions on Consumers.
+
+    Attributes:
+        perms_connect (list): Required permissions to connect to this
+            consumer.
+
+    """
+    http_user = True  # Enable message.user
+    perms_connect = []
+
+    def connect(self, message, **kwargs):
+        """Check permissions on connection."""
+        if message.user.has_perms(self.perms_connect):
+            super().connect(message, **kwargs)
+        else:
+            self.close()
+
+
+class KPsul(PermConsumerMixin, DjangoJsonWebsocketConsumer):
     groups = ['kfet.kpsul']
+    perms_connect = ['kfet.is_team']