In simple terms, authentication is the process of establishing the truth of an entity. Here, the entity could be a user or service on the network. For example, when you log in to your e-mail account, the e-mail server authenticates you based on your username and password. In almost every organization, the users who are part of the organization's network need to be authenticated before they are able to successfully log on to the network. Once the user is authenticated, the user should be restricted to use only the services to which the user is authorized. Authorization defines all the resources that a user can access or use. An example of the authorization is clearly visible on a Linux system. Every file and directory has permissions associated with them. These permissions decide which user can read, write, or access the file or directory.