* add expiry time to webhook user info
This also adds an optional message to webhook errors: if we fail to
parse an expiry time, we will log a warning with the parse error.
* refactored Auth
This change had one main goal: put in common all expiry time
extraction code between the JWT and WebHook parts of the
code. Furthermore, this change also moves all WebHook specific code to
its own module, similarly to what is done for JWT.
* Remove dependency on string-conversions in favor of text-conversions
string-conversions silently uses UTF8 instead of being explicit about
it, and it uses lenientDecode when decoding ByteStrings when it’s
usually better to reject invalid UTF8 input outright. text-conversions
solves both those problems.
Co-authored-by: Alexis King <lexi.lambda@gmail.com>
