You would have to ask the owner of the server about that, it varies between servers.
Chat with our AI personalities
you have to be the server owner to change it.
You can crack it by go to server properties and change to offline mode there you go.
A dedicated Minecraft server is a server where you can play original Minecraft. Usually without plugins or mods.
To make a private server, you will need to go to your server.properties file and change it to whitelist true.
Minecraft 1.2.3 is a game version, not a server.