An expression like `force_bytes(chr(...))`, on Python 3 where the
`force_bytes` finds itself with something to do because `chr` returns
a text string, gives the UTF-8 encoding of the given value as a
Unicode codepoint.
Here, we don't want that -- rather we want the given value as a
single byte. We can do that with `struct.pack`.
This fixes an issue where the "Link with Webathena" flow was producing
invalid credential caches when run on Python 3, breaking the Zephyr
mirror for any user who went through it anew.
This shows up when you're not running a Zephyr mirroring bot and lets
you use Webathena to have us run it. Obviously needs more docs.
Current problems include:
* supervisorctl reload ends up recreating /var/run/supervisor.sock
with the wrong permissions, so it only works once in a row before
you need to chmod that.
* /etc/supervisor/conf.d needs to be humbug-writeable; this is a clear
local root vulnerability
* This uses SSH and thus is kinda slow.
(imported from commit 7029979615ffd50b10f126ce2cf9a85a5eefd7a2)