Sign-in with Ethereum (SIWE) support for supabase auth

SIWE is an authentication method, very similar (in threat modelling terms) to WebAuthN that has been adopted by auth0 - and is used in the web3 scene to extend dApp functionality. It'd be nice to support SIWE as an auth provider for supabase. I'm not fluent enough in go to handle the nonce generation part in the gotrue repo so I just leave a guide here on how authentication looks like on frontend and backend for SIWE: Basically the backend generates a cryptographically secure nonce, which the client signs as: Once the backend verifies the signature - (that it belongs to its domain, nonce and timestamp is valid etc) it can map a session token to the user wallet that signed the message: `javascript import { SiweMessage } from 'siwe' const handler = async (request, response) => { try { const { message, signature } = request.body const siweMessage = new SiweMessage(message) const fields = await siweMe…