feat(auth): implement user authentication system

backend/node_modules/jsonwebtoken/lib/NotBeforeError.js

@@ -0,0 +1,13 @@
+var JsonWebTokenError = require('./JsonWebTokenError');
+
+var NotBeforeError = function (message, date) {
+  JsonWebTokenError.call(this, message);
+  this.name = 'NotBeforeError';
+  this.date = date;
+};
+
+NotBeforeError.prototype = Object.create(JsonWebTokenError.prototype);
+
+NotBeforeError.prototype.constructor = NotBeforeError;
+
+module.exports = NotBeforeError;