added simplistic dictionary_auth example (#105)

demo/dictionary_auth/authz.py

@@ -0,0 +1,34 @@
+from aiohttp_security.abc import AbstractAuthorizationPolicy
+
+
+class DictionaryAuthorizationPolicy(AbstractAuthorizationPolicy):
+    def __init__(self, user_map):
+        super().__init__()
+        self.user_map = user_map
+
+    async def authorized_userid(self, identity):
+        """Retrieve authorized user id.
+        Return the user_id of the user identified by the identity
+        or 'None' if no user exists related to the identity.
+        """
+        if identity in self.user_map:
+            return identity
+
+    async def permits(self, identity, permission, context=None):
+        """Check user permissions.
+        Return True if the identity is allowed the permission in the
+        current context, else return False.
+        """
+        # pylint: disable=unused-argument
+        user = self.user_map.get(identity)
+        if not user:
+            return False
+        return permission in user.permissions
+
+
+async def check_credentials(user_map, username, password):
+    user = user_map.get(username)
+    if not user:
+        return False
+
+    return user.password == password