How to log-in to an existing GitHub account?

[MattHeslington]

Hello,
I've added the GitHub oauth provider and am able to get everything working correctly for new signups. However, when a user who already has an account through a GitHub signup tries to log-in, I get a 'new LuciaError("AUTH_INVALID_USER_ID")' and I'm not quite sure what to do.

Both new GitHub users and returning users login/signup through a button which points to my oauth endpoint (is this correct?):

<a href="/api/oauth">Continue with Github</a>

When a returning user tries to login, we're getting the code and state from GitHub - this is the url shown in the browser, yet it's throwing the above error:

http://localhost:5173/api/oauth/github?code=831301d2bc82e6c6e4e5&state=xphqKNfkzctH8rKib0nwbPcjZk2HBPp3Wsc9X48xvQ7

This is my /api/oauth/github file:

export const GET = async ({ cookies, url, locals }) => {
    // get code and state params from url
    const code = url.searchParams.get('code')
    const state = url.searchParams.get('state')

    // get stored state from cookies
    const storedState = cookies.get('github_oauth_state')

    // validate state
    if (!state || !storedState || state !== storedState) {
        throw new Response(null, { status: 401 })
    }

    try {
        console.log('try github')
        const { existingUser, providerUser, createUser } = await githubAuth.validateCallback(code)

        const getUser = async () => {
            if (existingUser) {
                console.log('existingUser', existingUser)
                return {
                    existingUser,
                }
            }
            // create a new user if the user does not exist
            console.log('createUser')
            return await createUser({
                // attributes
                username: providerUser.login,
            })
        }
        console.log('before getUser')
        const user = await getUser()
        console.log('after getUser', user)
        const session = await auth.createSession(user.userId)
        locals.auth.setSession(session)
    } catch (e) {
        // invalid code
        console.log('catch', e)
        return new Response(null, {
            status: 500,
        })
    }
    throw redirect(302, '/')
}

The line console.log('after getUser', user) outputs correctly, yet I'm still getting the error, as do all the console logs, but there's no error logged from the catch.

Can anyone see any obvious mistakes I'm making please?
Cheers, Matt

[MattHeslington]

The 'try' statement was wrong. This works:

try {
        const { existingUser, providerUser, createUser } = await githubAuth.validateCallback(code)
        const user =
            existingUser ??
            (await createUser({
                username: providerUser.login,
                ...
            }))
        const session = await auth.createSession(user.userId)
        locals.auth.setSession(session)
    }