UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(username, password);

This line of code creates a new instance of the UsernamePasswordAuthenticationToken class and initializes it with the provided username and password. This object is typically used to represent a user's authentication request, which can be passed to an authentication manager or provider for verification. Once the user's credentials are validated, the authentication token can be updated with additional information about the user, such as their roles or authorities, before being returned to the application.