facebookAuth.js

const credentials = require( './credentials.json' ).facebook

const { client_id, client_secret } = credentials;

var fetch = require( 'node-fetch' );

module.exports.getUser = ( code ) => {

    let appToken;
    let url = 'https://graph.facebook.com/oauth/access_token?client_id=' + client_id + '&client_secret=' + client_secret + '&grant_type=client_credentials';
    //login as a facebook app to get an "app token"
    return fetch( url, { method: 'GET' } )
        .then( response => response.json() )
        .then( response => {
            appToken = response.access_token;
        //validate "social token", must pass the "app token"
            return fetch( 'https://graph.facebook.com/debug_token?input_token=' + code + '&access_token=' + appToken, {
                method: 'GET',
            } )
        } )
        .then( response => response.json() )
        .then( response => {
        //check the audience of the token
            const { app_id, is_valid, user_id } = response.data
            if ( app_id !== client_id ) {
                throw new Error( 'invalid app id: expected [' + client_id + '] but was [' + app_id + ']' );
            }
        //check if the token is valid
            if ( !is_valid ) {
                throw new Error( 'token is not valid' );
            }
        //get user profile using the app token
            return fetch( 'https://graph.facebook.com/v2.11/' + user_id + '?fields=id,name,picture,email&access_token=' + appToken, {
                method: 'GET',
            } )

        } )
        .then( response => response.json() )
        .then( response => {
        // return the user profile
            const { id, picture, email, name } = response;
            let user = {
                name: name,
                pic: picture.data.url,
                id: id,
                email_verified: true,
                email: email
            }
            return user;
        } )
//throw an error if something goes wrong
        .catch( err => {
            throw new Error( "error while authenticating facebook user: " + JSON.stringify( err ) );
        } );


}