Functionally identical, but more obviously cryptographically secure.
...Explicit is better than implicit?
Avoids needing to know that SystemRandom() implies a CSPRNG, and
complies with the big scary red box on the documentation for random:
> Warning:
> The pseudo-random generators of this module should not be used for
> security purposes. For security or cryptographic uses, see the
> secrets module.
https://docs.python.org/3/library/random.html
Signed-off-by: Dan Callahan <danc@element.io>
498084228b