The strategy of hex encoding a random byte array only uses the
following characters:

	0123456789abcdef

Instead of the entire bootstrapping token character set:

	0123456789abcdefghijklmnopqrstuvwxyz

Update the token generation to use the entire character set. This
increases the token secret from 48 bits of entropy to ~82 bits.

256^8 (1.8e+19) vs. 36^16 (7.9e+24).