diff --git a/keystonemiddleware/auth_token/__init__.py b/keystonemiddleware/auth_token/__init__.py
index 46a6b1e5..4ac73886 100644
--- a/keystonemiddleware/auth_token/__init__.py
+++ b/keystonemiddleware/auth_token/__init__.py
@@ -548,7 +548,7 @@ class AuthProtocol(BaseAuthProtocol):
                                    _base.AUTHTOKEN_GROUP,
                                    list_opts(),
                                    conf)
-        if self._conf.oslo_conf_obj != cfg.CONF:
+        if self._conf.oslo_conf_obj is not cfg.CONF:
             oslo_cache.configure(self._conf.oslo_conf_obj)
 
         token_roles_required = self._conf.get('service_token_roles_required')
diff --git a/keystonemiddleware/tests/unit/auth_token/test_config.py b/keystonemiddleware/tests/unit/auth_token/test_config.py
index 6b824afe..6a253a11 100644
--- a/keystonemiddleware/tests/unit/auth_token/test_config.py
+++ b/keystonemiddleware/tests/unit/auth_token/test_config.py
@@ -60,7 +60,9 @@ class TestAuthPluginLocalOsloConfig(base.BaseAuthTokenTestCase):
             'password': uuid.uuid4().hex,
         }
 
-        content = ("[keystone_authtoken]\n"
+        content = ("[DEFAULT]\n"
+                   "test_opt=15\n"
+                   "[keystone_authtoken]\n"
                    "auth_type=%(auth_type)s\n"
                    "www_authenticate_uri=%(www_authenticate_uri)s\n"
                    "auth_url=%(www_authenticate_uri)s\n"
@@ -99,6 +101,16 @@ class TestAuthPluginLocalOsloConfig(base.BaseAuthTokenTestCase):
             self.assertEqual(self.oslo_options[option],
                              conf_get(app, option))
 
+    def test_passed_oslo_configuration_with_deprecated_ones(self):
+        deprecated_opt = cfg.IntOpt('test_opt', deprecated_for_removal=True)
+        cfg.CONF.register_opt(deprecated_opt)
+        cfg.CONF(args=[],
+                 default_config_files=[self.conf_file_fixture.path])
+        conf = {'oslo_config_config': cfg.CONF}
+
+        # success to init AuthProtocol
+        self._create_app(conf)
+
     def test_passed_oslo_configuration_wins(self):
         """oslo_config_config has precedence over oslo_config_project."""
         conf = {'oslo_config_project': self.project,
diff --git a/releasenotes/notes/bug-1789351-102e2e5119be38b4.yaml b/releasenotes/notes/bug-1789351-102e2e5119be38b4.yaml
new file mode 100644
index 00000000..65f5555f
--- /dev/null
+++ b/releasenotes/notes/bug-1789351-102e2e5119be38b4.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - >
+    [`bug 1789351 <https://bugs.launchpad.net/keystonemiddleware/+bug/1789351>`_]
+    Fixed the bug that when initialize `AuthProtocol`, it'll raise "dictionary
+    changed size during iteration" error if the input `CONF` object contains
+    deprecated options.