01-14-2015, 03:01 AM
When the server is in online mode, it checks each incoming player by contacting Mojang auth server and asking if such a client asked to join the server (http://wiki.vg/Protocol_Encryption#Server )
So in order to join a server in online mode, the client first needs to inform the Mojang auth servers that it's gonna join the server. ( http://wiki.vg/Protocol_Encryption#Client )
The message that informs Mojang auth server about the client joining contains the user's "access token", which the client only receives when it authenticates with the auth servers before starting MineCraft (in the launcher, http://wiki.vg/Authentication#Authenticate )
So in order to join a server in online mode, the client first needs to inform the Mojang auth servers that it's gonna join the server. ( http://wiki.vg/Protocol_Encryption#Client )
The message that informs Mojang auth server about the client joining contains the user's "access token", which the client only receives when it authenticates with the auth servers before starting MineCraft (in the launcher, http://wiki.vg/Authentication#Authenticate )