It sounds like the "Admin Login" plugin you're describing is an alternative way to authenticate and grant admin access to players on your server, rather than using the traditional method of setting a password with the "setinfo _pw" command. The plugin would read admin information from an "admin_data.ini" file, and prompt players for their password upon connecting to the server. This is a useful feature as it allows you to manage admin access through a file rather than having to manually set passwords for each admin via the console.