Add client model

src/libs/models/client.js

+const mongoose = require('mongoose');
+const Schema = mongoose.Schema;
+
+let Client = new Schema({
+    name: {
+        type: String,
+        unique: true,
+        required: true
+    },
+    clientSecret: {
+        type: String,
+        required: true,
+        unique: true
+    }
+});
+
+module.exports = mongoose.model('Client', Client);