[Suggestion] Automatically provide a valid access token without server exchange

[maiconcarraro]

Use case

The proposal in README already is "The Embedded App SDK handles the communication between Discord and your iframed application", expectations would be to allow developers to create solo client side apps without the need to spin up a server only to exchange the code<>token.

As example, Twitch extensions automatically generate a valid user access token once they accept to share the scope, this allows to skip the server and build fully static deployed apps while still making requests to the discord API from the client.

For specific cases where you need to fetch external data, do special validations, you could reuse the token like Twitch, check integrity (using secret id) and allow/deny actions. (This being an optional flow)