Access current JWT data in JWT callback (social account linking)

[borgbob]

Goals

1. Implement social account linking by combining logins from multiple accounts into one JWT

Non-Goals

No response

Background

I'm working on an app which uses the credentials provider as the main way to sign in, but I also want to allow the user linking multiple social accounts.

When signing with a different provider, the JWT data is replaced, which makes linking data from multiple accounts into one JWT difficult.

Proposal

I can currently make this work by implementing the jwt callback and parsing the current session cookies to generate the combined JWT

     async jwt({ token, user, trigger, account, profile }) {
      if (trigger !== 'signIn' || !user) {
        return token
      }

      if (account?.provider === 'credentials') {
        // logging in with credentials
        return token
      }

      const provider = account?.provider
      if (!provider) {
        return token
      }

      const sessionCookie = cookies().get("authjs.session-token")?.value
      if (!sessionCookie) {
        console.warn('No session cookie found')
        return token
      }

      const secret = process.env.AUTH_SECRET
      // the "verify" function will decrypt/verify the session cookie
      const currentJwt = await verify(secret, sessionCookie)

      const linkedAccounts = (currentJwt.linkedAccounts ?? {}) as Record<string, string>
      switch (provider) {
        case 'github':
          linkedAccounts[provider] = profile?.login as string
          break;
        case 'twitter':
          linkedAccounts[provider] = (profile?.data as any)?.username as string
          break;
        default:
          console.warn('Unknown provider', provider, profile)
          break;
      }

      return {
        ...currentJwt,
        linkedAccounts
      }
    }

While the above works fine for me, it seems a bit redundant that I have to re-parse the JWT from the current session. What I would like is for the currentJwt to be available as a parameter to the jwt callback (I assume the data is already available in the context that calls the jwt function).

I'm rather new to next-auth, so if there's a simpler way to do social account linking, please let me know. My prior search led to #1702