diff --git a/bp/auth/routes.py b/bp/auth/routes.py
index ad0d600..658a954 100644
--- a/bp/auth/routes.py
+++ b/bp/auth/routes.py
@@ -49,6 +49,9 @@ def register(url_prefix="/auth"):
     @auth_bp.get("/login/")
     async def login_form():
         store_login_redirect_target()
+        cross_cart_sid = request.args.get("cart_sid")
+        if cross_cart_sid:
+            qsession["cart_sid"] = cross_cart_sid
         if g.get("user"):
             return redirect(federation_url("/"))
         return await render_template("auth/login.html")
diff --git a/shared b/shared
index 07aa2e2..1c1ab35 160000
--- a/shared
+++ b/shared
@@ -1 +1 @@
-Subproject commit 07aa2e2be90c134099077263b300fca7a83cdc0e
+Subproject commit 1c1ab3576f2ac661f454bdff88749ebc8eb70e32