HTML forms with EDS?

Question

Electronic digital signature

There was a need in one of the projects to implement the mechanism of Electronic Digital Signatures. That is, it is necessary that the data (sent by the user through forms) be signed with an EDS and verified on the server.
Google managed only a general understanding of the work of this whole thing + a couple of recipes for creating and issuing certificates to clients.
But important pieces of the puzzle are missing:
Is it possible to sign EDS web forms not only from IE under Win + CAPICOM.DLL, but, for example, from under nix systems and from macs?
How are web forms signed? JavaScript? Do they sign themselves (the main thing is to call the hidden field correctly)?
Is it possible to do all this cross-platform and free of charge with your own hands (let the hands be straight and there will be 6 of them)?

Answer 1

Regarding your third question:
CryptoPro already offers a plug-in that allows you to sign documents in all existing common browsers.