feat(auth): implement user authentication system

backend/node_modules/jsonwebtoken/lib/timespan.js

@@ -0,0 +1,18 @@
+var ms = require('ms');
+
+module.exports = function (time, iat) {
+  var timestamp = iat || Math.floor(Date.now() / 1000);
+
+  if (typeof time === 'string') {
+    var milliseconds = ms(time);
+    if (typeof milliseconds === 'undefined') {
+      return;
+    }
+    return Math.floor(timestamp + milliseconds / 1000);
+  } else if (typeof time === 'number') {
+    return timestamp + time;
+  } else {
+    return;
+  }
+
+};