[boredpenguin]

> doesn't already have a way to sign, verify, encrypt and decrypt text.

I know it's not exactly that, but if anyone wants to use PGP in the browser with webmail clients, there's Mailvelope[0].

What I like about it is that you can use it with GnuPG as a backend[1], so I can sign and decrypt emails in the browser with an OpenPGP smartcard without importing private keys.

[0]: https://www.mailvelope.com

[1]: https://www.mailvelope.com/en/faq#gnupg