What Is a User?
A user is an individual or application program identity that has been defined in the GlassFish Server. In a web application, a user can have associated with that identity a set of roles that entitle the user to access all resources protected by those roles. Users can be associated with a group.

A Java EE user is similar to an operating system user. Typically, both types of users represent people. However, these two types of users are not the same. The Java EE server authentication service has no knowledge of the user name and password you provide when you log in to the operating system. The Java EE server authentication service is not connected to the security mechanism of the operating system. The two security services manage users that belong to different realms.

What Is a Group?
A group is a set of authenticated users, classified by common traits, defined in the GlassFish Server. A Java EE user of the file realm can belong to a group on the GlassFish Server. (A user in the certificate realm cannot.) A group on the GlassFish Server is a category of users classified by common traits, such as job title or customer profile. For example, most customers of an e-commerce application might belong to the CUSTOMER group, but the big spenders would belong to the PREFERRED group. Categorizing users into groups makes it easier to control the access of large numbers of users.

A group on the GlassFish Server has a different scope from a role. A group is designated for the entire GlassFish Server, whereas a role is associated only with a specific application in the GlassFish Server.

What Is a Role?
A role is an abstract name for the permission to access a particular set of resources in an application. A role can be compared to a key that can open a lock. Many people might have a copy of the key. The lock doesn’t care who you are, only that you have the right key.

 
 <security-role-mapping>
    <role-name>RoleUSER</role-name>
    <principal-name>USERPrincipal</principal-name>
    <group-name>USERGroup</group-name>
  </security-role-mapping>