Add support for email retrieval on sign in for X/ Twitter Oauth 2.0

[alfredsadjei]

Goals

1. Allow for user email retrieval on sign in using the Twitter provider

Non-Goals

No response

Background

Currently Auth.js does not support email retrieval on sign in for Twitter/X OAuth 2.0. Given that this feature is now supported by X API V2, it would be great to have this supported by Auth.js as well.

Proposal

Given that the profile callback on the OAuth2Config<Profile> interface accepts both the entire profile retrieved by the OAuth provider as well as the retrieved token set, by modifying the twitter provider's auth scope ;

...
    authorization: "https://x.com/i/oauth2/authorize?scope=users.read tweet.read users.email offline.access",
...

we are able to simply fetch the user email (as described by x devs) and attach the resulting email data to the returned user object.

...
    async profile(profile, tokens) {
      const x_api_v2_email = await retrieveEmailForXApiV2(tokens.access_token)
      return {
        id: profile.data.id,
        name: profile.data.name,
        email: x_api_v2_email ?? null,
        image: profile.data.profile_image_url,
      }
    },

packages/core/src/lib/utils/providers.ts

export async function retrieveEmailForXApiV2(
  accessToken: string | undefined
): Promise<any | undefined> {
  if (!accessToken) return undefined
  const response = await fetch(
    "https://api.twitter.com/2/users/me?user.fields=confirmed_email",
    {
      headers: {
        Authorization: `Bearer ${accessToken}`,
      },
    }
  )
  const { data } = await response.json()
  return data.confirmed_email
}

Yes, I would be willing to contribute with a PR.