Support reading the challenge-response from console

Support reading the challenge-response from console

Trying to keep the footrpint small, this patch adds to the
convoluted code-flow in get_user_pass_cr(). Cleanup left for later.
-----8<-----

Currently prompting for a response to static-challenge
gets skipped when the username and passowrd are read
from a file. Further, dynamic challenge gets wrongly handled
as if its a username/password request.

The Fix:
- Add yet another flag in get_user_pass_cr() to
  set when prompting of response from console is needed.
- In receive_auth_failed(), the challenge text received
  from server _always_ copied to  the auth_challenge
  buffer: this is needed to trigger prompting from console
  when required.
- Also show the challenge text instead of an opaque
  "Response:" at the prompt.

While at it, also remove the special treatment of authfile ==
"management" in get_user_pass_cr(). The feature implied by that
test does not exist.

Tested:
  - username and optionally password from file, rest from console
  - the above with a static challenge
  - the above with a dynamic challenge
  - all of the above with systemd in place of console
  - all from management with and without static/dynamic
    challenge.

Thanks to Wayne Davison <wayne@opencoder.net> for pointing out the
issue with challenge-response, and an initial patch.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1450638773-11376-1-git-send-email-selva.nair@gmail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/10868
Signed-off-by: Gert Doering <gert@greenie.muc.de>