Add support Discord Oauth2

[Angelisium]

It would be nice to add discord.

I had a quick look, discord uses a classic OAuth2 system (RFC 6749) so I guess it should be trivial to add.

A small excerpt from the doc (to save you time):

OAuth2 URLs	description
https://discord.com/oauth2/authorize	Base authorization URL
https://discord.com/api/oauth2/token	Token URL
https://discord.com/api/oauth2/token/revoke	Token Revocation URL

Scope needed to solve the identity => identify and email Get Current User : (GET) /users/@me

Thank for ur work 💖

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