Dedicated error code for failed 3pid auth verification

synapse/api/errors.py

@@ -39,6 +39,7 @@ class Codes(object):
     MISSING_PARAM = "M_MISSING_PARAM",
     TOO_LARGE = "M_TOO_LARGE",
     EXCLUSIVE = "M_EXCLUSIVE"
+    THREEPID_AUTH_FAILED = "M_THREEPID_AUTH_FAILED"
 
 
 class CodeMessageException(RuntimeError):

synapse/rest/client/v2_alpha/account.py

@@ -126,7 +126,9 @@ class ThreepidRestServlet(RestServlet):
         threepid = yield self.identity_handler.threepid_from_creds(threePidCreds)
 
         if not threepid:
-            raise SynapseError(400, "Failed to auth 3pid")
+            raise SynapseError(
+                400, "Failed to auth 3pid", Codes.THREEPID_AUTH_FAILED
+            )
 
         for reqd in ['medium', 'address', 'validatedAt']:
             if reqd not in threepid: