authpolicy: Assume single-user

Assume AuthenticateUser, GetUserStatus etc. is only ever called with
one account id and crash if not (for security reasons). Chrome should
make sure this is the case. On user switch, authpolicyd should be
restarted.

The old code kept an account id -> data map, but multiple account ids
have never been properly supported since authpolicyd only keeps track
of one TGT at a time (authenticating with another user wipes krb5cc).

BUG=chromium:555491
TEST=cros_run_unit_tests --board=amd64-generic --packages authpolicy

Change-Id: I230e21f8341d3fed50dd5a77f9081e954c89b81b
Reviewed-on: https://chromium-review.googlesource.com/571225
Commit-Ready: Lutz Justen <ljusten@chromium.org>
Tested-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Roman Sorokin <rsorokin@chromium.org>
5 files changed