This final post in a series guides readers through building a full-stack MERN app utilizing JWT authentication, emphasizing server-side user validation and JWT generation. The process starts with creating a user store and validating user credentials, responding with appropriate messages if the credentials are incorrect or if the user is not found. A new authentication service, AuthUser, is introduced to handle server communication, and subsequent client-side logic updates include decoding JWTs and storing them in localStorage for session persistence. Error handling improvements are also discussed, ensuring messages are cleared during successful events, and the article touches on deploying the app using React’s production build and Heroku. The post underscores the importance of handling JWTs securely, without exposing sensitive data like passwords in plaintext.