Sveltekit Discord Oauth2

Uses v10 of Discord API.

Uses this SvelteKit template.

Hey, I don't understand anything, OAuth2 confuses me :(

This is why I am here. Let's take this step by step :)

First you have to do a few things

1. Create an app on discord.com/developers.
2. On the OAuth2 settings tab, create a new Redirect URI with this value http://localhost:3000/api/v1/user/auth. This is our API endpoint in which we will authenticate the user.
3. Under the URL generator settings tab, click the identify scope and the guilds scope.
4. Add the generated URL in the Login with Discord button's click event.
5. Get the app's client ID and client secret in the OAuth2 settings tab and...
6. Create a .env file in the root of the directory and add the following lines, adding the values from step 2 and step 5 between the "".

   DISCORD_REDIRECT_URI=""
   DISCORD_OAUTH_CLIENT_ID=""
   DISCORD_OAUTH_CLIENT_SECRET=""
   

In production change the localhost:3000 with your domain on discord.com/developers AND generate a new authorization URL.

The authentication process

1. User clicks the Login with Discord button and they get redirected to the generated URL.
2. Assuming they authorized our app in the Discord website, they will be redirected to out Redirect URI, which is our endpoint(http://localhost:3000/api/v1/user/auth in this case). Discord will append a code query parameter that we can use to get user data from Discord's API.
3. In our endpoint we get the user data and the guilds they are in, then we create a new session in memory(with sessionHandler) and saving the user data in it. Creating a session will return us a random ID that will send back to the user as a cookie, just as we redirect them to /dashboard. That is so...
4. When a user navigates to a protected route(eg. the dashboard folder), they send the cookie(automatically), then the cookie gets parsed in /src/hooks.ts, and then authenticated in the /src/routes/dashboard/__layout.svelte.
5. And now, navigating to localhost:3000/dashboard should display the user's Discord ID.

FullUser is the aggregated result of the authenticated user's access token data(GrantData) and user information data(UserData).

Contributions welcome