Abstract: An authentication system includes a storage device, an authentication server, a work server, and a user device. The authentication server communicates with the storage device. The work server communicates with the authentication server. The user device communicates with the authentication server and the work server. The user device logins in the authentication server and obtains an authentication token from the authentication server. The authentication server obtains an information from the storage device and transmits the information to the work server. The user device transmits the authentication token to the authentication server through the work server to perform authentication. The work server obtains an authentication result from the authentication server. When the authentication result is correct, the work server performs an operation request of the user device for the information.