diff --git a/addons/web/controllers/home.py b/addons/web/controllers/home.py
index 7b46be35d32..2483da10e02 100644
--- a/addons/web/controllers/home.py
+++ b/addons/web/controllers/home.py
@@ -88,9 +88,15 @@ class Home(http.Controller):
         if request.httprequest.method == 'GET' and redirect and request.session.uid:
             return request.redirect(redirect)
 
-        # so it is correct if overloaded with auth="public"
-        if not request.uid:
-            request.update_env(user=odoo.SUPERUSER_ID)
+        # simulate hybrid auth=user/auth=public, despite using auth=none to be able
+        # to redirect users when no db is selected - cfr ensure_db()
+        if request.env.uid is None:
+            if request.session.uid is None:
+                # no user -> auth=public with specific website public user
+                request.env["ir.http"]._auth_method_public()
+            else:
+                # auth=user
+                request.update_env(user=request.session.uid)
 
         values = {k: v for k, v in request.params.items() if k in SIGN_UP_REQUEST_PARAMS}
         try: