[afgrant]

The hazard of base64 is the use of '+', '/', and '=' characters, which most HTTP engines treat as special.

[Macha]

Luckily the spec provides for a url safe variant (sometimes called base64url): https://datatracker.ietf.org/doc/html/rfc4648#section-5

[afgrant]

It exists, but I wouldn’t call that “lucky”, or a selling point.