Web server app using sdk

I am trying to use the ring central javascript sdk. My created up is for our users only, it is a web server app. I am not clear on how needs to be used to log in and run an endpoint.

I am running this but I keep getting unauthorized for this grant type.

let rcsdk = new RC( {server: RINGCENTRAL_SERVER, clientId: RINGCENTRAL_CLIENTID, clientSecret: RINGCENTRAL_CLIENTSECRET} );
rcsdk
    .login({
        username: 'myusername', // phone number in full format
        extension: '', // leave blank if direct number is used
        password: 'mypassword'
    })
    .then(function(response) {
        console.log(response)
    })
    .catch(function(e) {
        console.log(e.message)
    });

any idea?