Inlined credentials: read missing password from management interface

Inlined credentials: read missing password from management interface

When commit 39619b7fab added support for inlining username only,
fallback for password was from console. This is not ideal when
graphical UI is in use as there is no console. Instead, query the
management interface when possible.

This patch just extends a similar fix when username is read from
a file and password is missing. As before, any username read
from file or inlined is not peserved as we currently have no way
of locking the username in the management interface prompt.

Change-Id: Ieeb2f980330d485739dbf3d722f107c1dbf704fc
Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1599
Message-Id: <20260414055900.17132-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg36608.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 287acce1acaad25a92f2112e967b9686418ef72a)