Set your server to online-mode=true and if they log in, they've paid! to be serious, there was a api at minecraft.net for that but since the updated the site that seems to be gone.
no no, you did not understand, use an authentication system and want to do an automatic authentication for paid players. I wonder how can I check if the player is entering the server using a unique launcher minecraft!
I'm using Offline Mode and I want when the player is Premium not need to use commands to authenticate
Code (rules (Unknown Language)): Discussion or distribution of illegal content is not permitted in any form. [*] This includes but is not limited to pirated content, nulled licenses for paid software, or anything where it could be deemed illegal. You're trying to get help and/or discuss illegal content. Not paying for the software is illegal EDIT: Snip'd
