Add 'credential' method on 'Policy' w/ consistency tests

nucypher/policy/policies.py

@@ -302,6 +302,22 @@ class Policy(ABC):
         """
         return self.publish_treasure_map(network_middleware=network_middleware)
 
+    def credential(self, with_treasure_map=True):
+        """
+        Creates a PolicyCredential for portable access to the policy via
+        Alice or Bob. By default, it will include the treasure_map for the
+        policy unless `with_treasure_map` is False.
+        """
+        from nucypher.policy.collections import PolicyCredential
+
+        treasure_map = self.treasure_map
+        if not with_treasure_map:
+            treasure_map = None
+
+        return PolicyCredential(self.alice.stamp, self.label, self.expiration,
+                                self.public_key, treasure_map)
+
+
     def __assign_kfrags(self) -> Generator[Arrangement, None, None]:
 
         if len(self._accepted_arrangements) < self.n:

tests/characters/test_alice_can_grant_and_revoke.py

@@ -71,6 +71,17 @@ def test_decentralized_grant(blockchain_alice, blockchain_bob, agency):
 
         assert kfrag == retrieved_kfrag
 
+    # Check that the PolicyCredential is consistent to the new policy
+    credential = policy.credential()
+    assert credential.alice_verifying_key == policy.alice.stamp
+    assert credential.label == policy.label
+    assert credential.expiration == policy.expiration
+    assert credential.policy_pubkey == policy.public_key
+    assert credential.treasure_map == policy.treasure_map
+
+    credential = policy.credential(with_treasure_map=False)
+    assert credential.treasure_map is None
+
 
 @pytest.mark.usefixtures('federated_ursulas')
 def test_federated_grant(federated_alice, federated_bob):