From cc2bbcd4dce1f53dc057390cc740e25ba5e7fe64 Mon Sep 17 00:00:00 2001
From: "Olivier Wilkinson (reivilibre)" <oliverw@matrix.org>
Date: Thu, 9 Dec 2021 12:29:08 +0000
Subject: [PATCH] Switch to the 400 M_EXCLUSIVE error code for non-existent
 device IDs

This is as a result of a discussion on the MSC
---
 synapse/api/auth.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 65369afd13..fd48735e1c 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -347,9 +347,12 @@ class Auth:
                 effective_user_id, effective_device_id
             )
             if device_opt is None:
+                # For now, use 400 M_EXCLUSIVE if the device doesn't exist.
+                # This is an open thread of discussion on MSC3202 as of 2021-12-09.
                 raise AuthError(
-                    403,
+                    400,
                     f"Application service trying to use a device that doesn't exist ('{effective_device_id}' for {effective_user_id})",
+                    Codes.EXCLUSIVE,
                 )
 
         return effective_user_id, effective_device_id, app_service