Provide a helper to load a context from environment

The intention here is to provide better integration between what
oslo.context expects and what keystonemiddleware provides. As auth_token
middleware changes each service has to react independently to the new
options and the way they build contexts.

By providing a helper here we can improve the consistency across
services to standardize the options and provide a common way to react to
auth_token middleware improvements.

Change-Id: Ic590b3ee359e9a9c27eef3d11c0738066f475881

2 files changed, 49 insertions, 0 deletions

diff --git a/oslo_context/context.py b/oslo_context/context.py
index 5d06cb8..9dd4001 100644
--- a/oslo_context/context.py
+++ b/oslo_context/context.py
@@ -106,6 +106,28 @@ class RequestContext(object):
             request_id=ctx.get("request_id"),
             resource_uuid=ctx.get("resource_uuid"))
 
+    @classmethod
+    def from_environ(cls, environ, **kwargs):
+        """Load a context object from a request environment.
+
+        If keyword arguments are provided then they override the values in the
+        request environment.
+
+        :param environ: The environment dictionary associated with a request.
+        :type environ: dict
+        """
+        # Load a new context object from the environment variables set by
+        # auth_token middleware. See:
+        # http://docs.openstack.org/developer/keystonemiddleware/api/keystonemiddleware.auth_token.html#what-auth-token-adds-to-the-request-for-use-by-the-openstack-service
+        kwargs.setdefault('auth_token', environ.get('HTTP_X_AUTH_TOKEN'))
+        kwargs.setdefault('user', environ.get('HTTP_X_USER_ID'))
+        kwargs.setdefault('tenant', environ.get('HTTP_X_PROJECT_ID'))
+        kwargs.setdefault('user_domain', environ.get('HTTP_X_USER_DOMAIN_ID'))
+        kwargs.setdefault('project_domain',
+                          environ.get('HTTP_X_PROJECT_DOMAIN_ID'))
+
+        return cls(**kwargs)
+
 
 def get_admin_context(show_deleted=False):
     """Create an administrator context."""
diff --git a/oslo_context/tests/test_context.py b/oslo_context/tests/test_context.py
index 9e6b252..531d762 100644
--- a/oslo_context/tests/test_context.py
+++ b/oslo_context/tests/test_context.py
@@ -13,12 +13,18 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import uuid
+
 from oslotest import base as test_base
 
 from oslo_context import context
 from oslo_context import fixture
 
 
+class Object(object):
+    pass
+
+
 class ContextTest(test_base.BaseTestCase):
 
     def setUp(self):
@@ -92,3 +98,24 @@ class ContextTest(test_base.BaseTestCase):
         self.assertFalse(context.is_user_context(ctx))
         ctx = context.RequestContext(is_admin=False)
         self.assertTrue(context.is_user_context(ctx))
+
+    def test_from_environ_variables(self):
+        auth_token = uuid.uuid4().hex
+        user_id = uuid.uuid4().hex
+        project_id = uuid.uuid4().hex
+        user_domain_id = uuid.uuid4().hex
+        project_domain_id = uuid.uuid4().hex
+
+        environ = {'HTTP_X_AUTH_TOKEN': auth_token,
+                   'HTTP_X_USER_ID': user_id,
+                   'HTTP_X_PROJECT_ID': project_id,
+                   'HTTP_X_USER_DOMAIN_ID': user_domain_id,
+                   'HTTP_X_PROJECT_DOMAIN_ID': project_domain_id}
+
+        ctx = context.RequestContext.from_environ(environ)
+
+        self.assertEqual(auth_token, ctx.auth_token)
+        self.assertEqual(user_id, ctx.user)
+        self.assertEqual(project_id, ctx.tenant)
+        self.assertEqual(user_domain_id, ctx.user_domain)
+        self.assertEqual(project_domain_id, ctx.project_domain)