Sign in with Apple Server Handler

app.js

const express = require('express')
const request = require('request')
const jwt = require('jsonwebtoken')
const jose = require('jose')
const app = express()

let client_id = "AppBundleID" // Maybe from client

function generateClientSecret() {
    let private_key = "-----BEGIN PRIVATE KEY-----\n......\n-----END PRIVATE KEY-----" // Should store in a safe place on server side
    
    // Generate client secret
    let client_secret = jwt.sign({
        iss: "YourTeamID", // Team ID, should store in server side
        sub: client_id, // Bundle ID, should store in server side
        aud: "https://appleid.apple.com", // Fix value
        iat: Math.floor(Date.now() / 1000),
        exp: Math.floor(Date.now() / 1000) + (60 * 60)
    }, private_key, {
        algorithm: 'ES256',
        header: {
            alg: 'ES256',
            kid: "YourKeyID" // Key ID, should store in a safe place on server side
        }
    })

    return client_secret
}

// Verify authorization api
app.get('/verify', function(req, res) {
    let code = req.query.code
    let userId = req.query.userid
    let token = req.query.token
    let email = req.query.email
    let familyName = req.query.family_name
    let givenName = req.query.given_name

    // Fetch public key from Apple
    request("https://appleid.apple.com/auth/keys", function(error, response, body) {
        let jwks = jose.JWKS.asKeyStore(JSON.parse(body))

        // JWS Verify
        if (jose.JWS.verify(token, jwks)) {
            console.log("ID Token has been Verified")
            let client_secret = generateClientSecret()
            
            // Request verification for apple api
            request.post({url: "https://appleid.apple.com/auth/token", form: {
                client_id: client_id,
                client_secret: client_secret,
                code: code,
                grant_type: "authorization_code"
            }}, function(err, response, body) {
                console.log(body)
                res.send(body)
            })
        } else {
            console.log("Cannot Verified ID Token")
            res.send(400)
        }
    })
})

// Refresh token demo api
app.get('/refresh', function(req, res) {
    let refreshToken = req.query.refresh_token

    let client_secret = generateClientSecret()
    request.post({
        url: "https://appleid.apple.com/auth/token", form: {
            client_id: client_id,
            client_secret: client_secret,
            grant_type: "refresh_token",
            refresh_token: refreshToken
        }
    }, function(err, response, body) {
        console.log(body)
        res.send(body)
    })
})

app.listen(8888)