s3-auth Hook checking passwords and generating session_info via the auth4_context

s3-auth Hook checking passwords and generating session_info via the auth4_context

This avoids creating a second auth_context, as it is a private pointer
in the auth4_context that has already been passed in, and makes the
gensec_ntlmssp code agnostic to the type of authentication backend
behind it. This will in turn allow the ntlmssp server code to be
further merged.

Andrew Bartlett

Signed-off-by: Stefan Metzmacher <metze@samba.org>