Do not copy auth_token username to itself

Do not copy auth_token username to itself

- Fixes a potential mis-behaviour (strncpy with
dest == src) introduced by commits ecad4839c (2.6)
and 3d792ae955 (2.5).
Reported by: Gert Doering <gert@greenie.muc.de>

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20221027160619.11894-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/search?l=mid&q=20221027160619.11894-1-selva.nair@gmail.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit dbf142ffe597b21aa09a47677ea2061b74a9354e)