Base64URL

[dcposch]

🧐 Motivation

OZ has a great Base64 encoder. (And, as far as I can tell, the only audited one.)

There's a lot of interest in passkey-based wallets now, which offer an excellent self-custody UX. These rely on the WebAuthn standard, which uses Base64URL.

For that use case and for completeness, it would be great to have a canonical, audited onchain Base64URL encoder.

📝 Details

Encoding	Input	Output
Base64	hello world	aGVsbG8gd29ybGQ=
Base64URL	hello world	aGVsbG8gd29ybGQ

I think this can be done with contract derived from Base64.sol with two straightforward modifications:

• Change two characters in the lookup table
• Remove the trailing = padding

If there's interest, I'm happy to send a PR.

[ernestognw]

Hey @dcposch, thanks for opening the issue. We agree this is an important use case and we're considering it for a future minor release.

For other readers, the two different characters for this version are -_ instead of +/ according to RFC4648.

This is being implemented through #4822 but we may want to also add a fuzz test suite for it after (and if) foundry-rs/foundry#6744 is solved.