Using an alternate base64 alphabet to encode data with the standard base64 algorithm is effectively the same as encrypting it with a long alphanumeric encryption key. We see this in common use in malware C2 channels. If we could supply a known alphabet to the base64 function, we could more easily decode some of the C2 channels. This would be of great benefit to many Bro users.
Ideally, I'd like to see something like:
const my_alphabet: string = "...";
decoded = decode_base64(data, my_alphabet);