feat!: Remove django-admin default login (#29876)

* feat!: Remove django-admin default login

cms/djangoapps/contentstore/views/public.py

@@ -7,12 +7,17 @@ from django.conf import settings
 from django.shortcuts import redirect
 from urllib.parse import quote_plus  # lint-amnesty, pylint: disable=wrong-import-order
 from waffle.decorators import waffle_switch
+from django.contrib import admin
 
 from common.djangoapps.edxmako.shortcuts import render_to_response
+from openedx.core.djangoapps.user_authn.config.waffle import ADMIN_AUTH_REDIRECT_TO_LMS
 
 from ..config import waffle
 
-__all__ = ['register_redirect_to_lms', 'login_redirect_to_lms', 'howitworks', 'accessibility']
+__all__ = [
+    'register_redirect_to_lms', 'login_redirect_to_lms', 'howitworks', 'accessibility',
+    'redirect_to_lms_login_for_admin',
+]
 
 
 def register_redirect_to_lms(request):
@@ -39,6 +44,16 @@ def login_redirect_to_lms(request):
     return redirect(login_url)
 
 
+def redirect_to_lms_login_for_admin(request):
+    """
+    This view redirect the admin/login url to the site's login page.
+    """
+    if ADMIN_AUTH_REDIRECT_TO_LMS.is_enabled():
+        return redirect('/login?next=/admin')
+    else:
+        return admin.site.login(request)
+
+
 def _build_next_param(request):
     """ Returns the next param to be used with login or register. """
     next_url = request.GET.get('next')