In terms of web applications, we have reached the stage where the application data doesn't only benefit you alone. It is often required to enable a third-party application access/usage of your backend applications and APIs to unleash the full potential of your application. For example, Twitter provides an API to grab its data (for an authenticated user, of course) and makes this usable for all third-party applications. Thus, there's always a reason to have a secure backend application or API.
Authentication simply means the action of proving or showing that something is true or valid. So, we can say that user authentication is the action of validating a user, while authorization is permitting or granting the user access to web resources, features, or pages. In the following section, we will be looking at how a user can be authenticated and authorized using a JSON Web Token.