Allow external EC key through --management-external-key

Allow external EC key through --management-external-key

- This automatically supports EC certificates through
  --management-external-cert
- EC signature request from management is prompted by
  >PK_SIGN if the client supports it (or >RSA_SIGN)
  Response should be of the form 'pk-sig' (or rsa-sig
  by older clients) followed by DER encoded signature
  as base64 terminated by 'END' on a new line.

v3: This is v2 adapted to the client_version capability
Requires pacthes 1 and 2 of the series 147:
https://patchwork.openvpn.net/project/openvpn2/list/?series=147

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1516909513-31683-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16365.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>