RFC2617 basic authorization header from username and password.

npm install basic-authorization-header --save

var basic = require('basic-authorization-header');
var headers = {
  'Authorization': basic("Aladdin", "open sesame"),
};

//=> { Authorization: 'Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==' }

• user: (String) username.
• pass: (String) password.

• (String) basic authorization header value.

• RFC2617
• Security Considerations
• Increasing Security
• http.request(options[, callback])

If you just want the token, check out basic-auth-token.