Created the session validation

validations/session.js

@@ -0,0 +1,12 @@
+const Joi = require('joi');
+
+// The validation used when creating a new session
+module.exports.create = Joi.object({
+    username: Joi.string()
+        .alphanum()
+        .min(5)
+        .max(15)
+        .required(),
+    password: Joi.string()
+        .required()
+});