add request validation to membership endpoint

utils/validateRequest.js

@@ -0,0 +1,12 @@
+var Joi = require('joi');
+
+module.exports = function validateRequest(schema) {
+  return function handler(req, res, next) {
+    Joi.validate(req.body, schema, function (err, value) {
+      if(err) {
+        return res.status(400).send(err.details)
+      }
+      next();
+    });
+  }
+}