Regarding the Radius authentication process, there are the following steps: 1. The Radius client (network access server) in the network device receives the username and password, and sends an authentication request to the Radius server; 2 the user logs in to the USG access server, etc. When the network device sends the username and password to the network access server; 3. After receiving the legitimate request, the Radius server completes the authentication and returns the required user authorization information to the client. What is the correct order?