diff --git a/tests/test_env.py b/tests/test_env.py
index ed79c37..1db85dc 100644
--- a/tests/test_env.py
+++ b/tests/test_env.py
@@ -24,6 +24,15 @@ class EnvTests(unittest.TestCase):
             "hello world", env.render_str({"name": "world"}, "hello {{ name }}")
         )
 
+    def test_common_domain(self):
+        self.assertEqual(
+            "mydomain.com",
+            env.render_str(
+                {"d1": "d1.mydomain.com", "d2": "d2.mydomain.com"},
+                "{{ d1|common_domain(d2) }}",
+            ),
+        )
+
     def test_render_str_missing_configuration(self):
         self.assertRaises(exceptions.TutorError, env.render_str, {}, "hello {{ name }}")
 
@@ -41,6 +50,12 @@ class EnvTests(unittest.TestCase):
         )
 
     def test_render_full(self):
+        defaults = tutor_config.load_defaults()
+        with tempfile.TemporaryDirectory() as root:
+            env.render_full(root, defaults)
+
+    def test_render_full_with_https(self):
+        defaults = tutor_config.load_defaults()
+        defaults["ACTIVATE_HTTPS"] = True
         with tempfile.TemporaryDirectory() as root:
-            defaults = tutor_config.load_defaults()
             env.render_full(root, defaults)
diff --git a/tutor/env.py b/tutor/env.py
index e89aff9..eb05121 100644
--- a/tutor/env.py
+++ b/tutor/env.py
@@ -25,7 +25,7 @@ class Renderer:
                 undefined=jinja2.StrictUndefined,
             )
             environment.filters["random_string"] = utils.random_string
-            environment.filters["common_domain"] = utils.random_string
+            environment.filters["common_domain"] = utils.common_domain
             environment.filters["reverse_host"] = utils.reverse_host
             environment.globals["TUTOR_VERSION"] = __version__
             cls.ENVIRONMENT = environment
@@ -68,22 +68,29 @@ def render_full(root, config):
     Render the full environment, including version information.
     """
     for subdir in ["android", "apps", "k8s", "local", "webui"]:
-        render_subdir(subdir, root, config)
+        save_subdir(subdir, root, config)
     copy_subdir("build", root)
-    render_file(config, VERSION_FILENAME)
+    save_file(VERSION_FILENAME, root, config)
 
 
-def render_subdir(subdir, root, config):
+def save_subdir(subdir, root, config):
     """
     Render the templates located in `subdir` and store them with the same
     hierarchy at `root`.
     """
     for path in walk_templates(subdir):
-        dst = pathjoin(root, path)
-        rendered = render_file(config, path)
-        utils.ensure_file_directory_exists(dst)
-        with open(dst, "w") as of:
-            of.write(rendered)
+        save_file(path, root, config)
+
+
+def save_file(path, root, config):
+    """
+    Render the template located in `path` and store it with the same hierarchy at `root`.
+    """
+    dst = pathjoin(root, path)
+    rendered = render_file(config, path)
+    utils.ensure_file_directory_exists(dst)
+    with open(dst, "w") as of:
+        of.write(rendered)
 
 
 def render_file(config, *path):
diff --git a/tutor/templates/apps/openedx/config/cms.env.json b/tutor/templates/apps/openedx/config/cms.env.json
index 50e108e..649e17a 100644
--- a/tutor/templates/apps/openedx/config/cms.env.json
+++ b/tutor/templates/apps/openedx/config/cms.env.json
@@ -33,7 +33,7 @@
   "EMAIL_PORT": {{ SMTP_PORT }},
   "HTTPS": "{{ "on" if ACTIVATE_HTTPS else "off" }}",
   "LANGUAGE_CODE": "{{ LANGUAGE_CODE }}",
-  {% if ACTIVATE_HTTPS %}"SESSION_COOKIE_DOMAIN": ".{{ lms_cms_common_domain }}",{% endif %}
+  {% if ACTIVATE_HTTPS %}"SESSION_COOKIE_DOMAIN": ".{{ LMS_HOST|common_domain(CMS_HOST) }}",{% endif %}
   "CACHES": {
     "default": {
       "KEY_PREFIX": "default",
diff --git a/tutor/templates/apps/openedx/config/lms.env.json b/tutor/templates/apps/openedx/config/lms.env.json
index 544c573..644fab8 100644
--- a/tutor/templates/apps/openedx/config/lms.env.json
+++ b/tutor/templates/apps/openedx/config/lms.env.json
@@ -44,7 +44,7 @@
   {% endif %}
   "LANGUAGE_CODE": "{{ LANGUAGE_CODE }}",
   "LOGIN_REDIRECT_WHITELIST": ["{{ CMS_HOST }}", "studio.localhost"],
-  {% if ACTIVATE_HTTPS %}"SESSION_COOKIE_DOMAIN": ".{{ lms_cms_common_domain }}",{% endif %}
+  {% if ACTIVATE_HTTPS %}"SESSION_COOKIE_DOMAIN": ".{{ LMS_HOST|common_domain(CMS_HOST) }}",{% endif %}
   "CACHES": {
     "default": {
       "KEY_PREFIX": "default",