Use Sessions URL from root service if it's provided

If the root endpoint provides the link to Sessions, we should just
use it.

Change-Id: I825930623c84d3b6e5994e29f963b4f5af7afe4d
Story: 2008059
Task: 40742

releasenotes/notes/use-sessions-url-from-root-8b8eca57dc450705.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Instead of trying to GET /redfish/v1/SessionService, which is usually
+    reachable via authentication, fail, and then guess
+    /redfish/v1/SessionService/Sessions as Sessions URL, we try first to use
+    directly the Sessions URL provided by the root service, if available.
+

sushy/auth.py

@@ -149,10 +149,18 @@ class SessionAuth(AuthBase):
         :raises: AccessError
         :raises: HTTPError
         """
+        target_uri = None
+        try:
+            target_uri = self._root_resource.get_sessions_path()
+        except exceptions.MissingAttributeError:
+            LOG.debug('Missing Sessions attribute under Links in Root '
+                      'Service, we\'ll try to determine it from Session '
+                      'Service')
         session_service = self._root_resource.get_session_service()
         session_auth_token, session_uri = (
             session_service.create_session(self._username,
-                                           self._password))
+                                           self._password,
+                                           target_uri=target_uri))
         self._session_key = session_auth_token
         self._session_resource_id = session_uri
         self._connector.set_http_session_auth(session_auth_token)

sushy/main.py

@@ -365,6 +365,16 @@ class Sushy(base.ResourceBase):
             self._conn, self._session_service_path,
             redfish_version=self.redfish_version)
 
+    def get_sessions_path(self):
+        """Returns the Sessions url"""
+
+        try:
+            links_url = self.json.get('Links')
+            return links_url['Sessions']['@odata.id']
+        except (TypeError, KeyError):
+            raise exceptions.MissingAttributeError(
+                attribute='Links/Sessions/@data.id', resource=self.path)
+
     def get_session(self, identity):
         """Given the identity return a Session object
 

sushy/resources/sessionservice/sessionservice.py

@@ -91,20 +91,26 @@ class SessionService(base.ResourceBase):
         """
         self._conn.delete(session_uri)
 
-    def create_session(self, username, password):
+    def create_session(self, username, password, target_uri=None):
         """This function will try to create a session.
 
+        :param username: the username of the user requesting a new session
+        :param password: the password associated to the user requesting
+            a new session
+        :param target_uri: the "Sessions" uri, usually in the form:
+            '/redfish/v1/SessionService/Sessions'
         :returns: A session key and uri in the form of a tuple
         :raises: MissingXAuthToken
         :raises: ConnectionError
         :raises: AccessError
         :raises: HTTPError
         """
-        try:
-            target_uri = self._get_sessions_collection_path()
-        except Exception:
-            # Defaulting to /Sessions
-            target_uri = self.path + '/Sessions'
+        if not target_uri:
+            try:
+                target_uri = self._get_sessions_collection_path()
+            except Exception:
+                # Defaulting to /Sessions
+                target_uri = self.path + '/Sessions'
 
         data = {'UserName': username, 'Password': password}
         LOG.debug("Requesting new session from %s.", target_uri)

sushy/tests/unit/test_main.py

@@ -390,6 +390,10 @@ class MainTestCase(base.TestCase):
         registries[1]
         self.assertEqual(1, mock_registries.__getitem__.call_count)
 
+    def test_get_sessions_path(self):
+        expected = '/redfish/v1/SessionService/Sessions'
+        self.assertEqual(expected, self.root.get_sessions_path())
+
 
 class BareMinimumMainTestCase(base.TestCase):
 
@@ -432,11 +436,15 @@ class BareMinimumMainTestCase(base.TestCase):
             exceptions.MissingAttributeError,
             'UpdateService/@odata.id', self.root.get_update_service)
 
-    def test_get_composition_service_when_compositionservice_attr_absent(
-        self):
+    def test_get_composition_service_when_compositionservice_attr_absent(self):
         self.assertRaisesRegex(
             exceptions.MissingAttributeError,
             'CompositionService/@odata.id', self.root.get_composition_service)
 
     def test__get_registry_collection_when_registries_attr_absent(self):
         self.assertIsNone(self.root._get_registry_collection())
+
+    def test_get_sessions_path_fail(self):
+        self.assertRaisesRegex(
+            exceptions.MissingAttributeError,
+            'Links/Sessions/@data.id', self.root.get_sessions_path)