Correct URL parsing logic (GoogleCloudPlatform#7530)

Co-authored-by: Dan Lee <[email protected]>

Author: glasnt

appengine/standard_python3/django/app.yaml

@@ -20,7 +20,7 @@ runtime: python39
 
 env_variables:
   # This setting is used in settings.py to configure your ALLOWED_HOSTS
-  # APPENGINE_URL: https://PROJECT_ID.uc.r.appspot.com
+  # APPENGINE_URL: PROJECT_ID.uc.r.appspot.com
 
 handlers:
 # This configures Google App Engine to serve the files in the app's static

appengine/standard_python3/django/mysite/settings.py

@@ -67,11 +67,12 @@
 # to App Engine. This code takes the URL and converts it to both these settings formats.
 APPENGINE_URL = env("APPENGINE_URL", default=None)
 if APPENGINE_URL:
-    # Ensure the HTTPS is in the URL before it's used.
-    APPENGINE_URL = urlparse(APPENGINE_URL, "https").geturl()
+    # Ensure a scheme is present in the URL before it's processed.
+    if not urlparse(APPENGINE_URL).scheme:
+        APPENGINE_URL = f"https://{APPENGINE_URL}"
 
-    ALLOWED_HOSTS = [APPENGINE_URL]
-    CSRF_TRUSTED_ORIGINS = [urlparse(APPENGINE_URL).netloc]
+    ALLOWED_HOSTS = [urlparse(APPENGINE_URL).netloc]
+    CSRF_TRUSTED_ORIGINS = [APPENGINE_URL]
     SECURE_SSL_REDIRECT = True
 else:
     ALLOWED_HOSTS = ["*"]