Use different secret for auth and access tokens

Temporarily secret guaranties invalidation of access tokens on device
reboot. Without that when device updates, we can have tokens signed
with valid key, but with invalid format, or user_id collision.

Change-Id: I0a6dbd782165715d781501456a4fd29bb060ffdd
Reviewed-on: https://weave-review.googlesource.com/2062
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
6 files changed