Use to_policy_values for policy credentials

The base oslo.context defines to_policy_values with all the information
that it expects a service to require to enforce policy. Use that instead
of throwing everything in to_dict at policy enforcement.

Change-Id: I0a42b4425e9dd1bd062c48792c4d116dd370afe3
Closes-Bug: #1602081

nova/context.py

@@ -277,6 +277,11 @@ class RequestContext(context.RequestContext):
                 raise
             return False
 
+    def to_policy_values(self):
+        policy = super(RequestContext, self).to_policy_values()
+        policy['is_admin'] = self.is_admin
+        return policy
+
     def __str__(self):
         return "<Context %s>" % self.to_dict()
 

nova/policy.py

@@ -152,7 +152,7 @@ def authorize(context, action, target, do_raise=True, exc=None):
            do_raise is False.
     """
     init()
-    credentials = context.to_dict()
+    credentials = context.to_policy_values()
     if not exc:
         exc = exception.PolicyNotAuthorized
     try:
@@ -177,7 +177,7 @@ def check_is_admin(context):
 
     init()
     # the target is user-self
-    credentials = context.to_dict()
+    credentials = context.to_policy_values()
     target = credentials
     return _ENFORCER.authorize('context_is_admin', target, credentials)