@Edent @Floppy @manyfold @robb wrote a blog post on implementing his own ActivityPub server in PHP (https://rknight.me/blog/building-an-activitypub-server/) - it includes a section on validating the signatures, because I think it was a major pain in the arse for him too (source code: https://github.com/rknightuk/bugle/blob/main/app/Services/HttpSignature.php)

@lewis @Edent @Floppy @manyfold Correct, it was in fact a huge pain to work out.