Using authlib-injector on a Minecraft server

Obtaining authlib-injector

First, you need to download the latest version of authlib-injector from here.

Vanilla server/Spigot/Paper/…

Since authlib-injector v1.2.0, you need to set enforce-secure-profile to true, which is different from previous versions!

If you encounter issues related to chat message signing on MC 1.19+, please read: 👉 authlib-injector v1.2.0 Upgrade FAQ #174 👈

Please set online-mode to true in the server’s server.properties. For 1.19+ servers, you also need to set enforce-secure-profile to true.

Then add the following JVM argument to the server’s startup command (the added argument should be placed before -jar):

-javaagent:{path/to/authlib-injector.jar}={https://your-yggdrasil-api-root.com}

• {path/to/authlib-injector.jar} indicates the location of the JAR file you downloaded in the previous step (either a relative or an absolute path is acceptable).
• {https://your-yggdrasil-api-root.com} indicates the URL of the authentication server.

For example, this is the original startup command:

java -jar minecraft_server.1.12.2.jar nogui

Assuming:

• The authlib-injector JAR file you downloaded is named authlib-injector.jar.
• You placed it in the same directory as the server JAR minecraft_server.1.12.2.jar.
• The authentication server URL is https://example.yggdrasil.yushi.moe.

Then the command line after adding the argument should be as follows:

java -javaagent:authlib-injector.jar=https://example.yggdrasil.yushi.moe -jar minecraft_server.1.12.2.jar nogui

BungeeCord/Velocity

If you are using BungeeCord or Velocity, then authlib-injector needs to be loaded on all servers as well as BungeeCord/Velocity (see the method above), and enforce-secure-chat should be enabled. However, only BungeeCord/Velocity should have online-mode enabled; the backend MC servers should have online-mode disabled.

Fetching Mojang Skins

After loading authlib-injector, all skins are fetched from the specified authentication server by default. For example:

• /give @p minecraft:skull 1 3 {SkullOwner:"notch"}
• (Citizens2 plugin) /npc skin notch

These commands fetch the skin of the character named notch from the custom authentication server.

If you want to use Mojang skins, you can append @mojang to the character name, such as:

• /give @p minecraft:skull 1 3 {SkullOwner:"notch@mojang"}
• /npc skin notch@mojang

For detailed instructions, see the -Dauthlibinjector.mojangNamespace option in README § Options.

Accessing Mojang via Proxy

The feature to fetch Mojang skins requires the MC server to be able to access the Mojang API. If your server needs to access Mojang through a proxy, you can add the following JVM argument at startup to specify the proxy:

-Dauthlibinjector.mojangProxy=socks://<host>:<port>

Note:

• This proxy is only used when querying character information from Mojang; texture image downloads do not go through the proxy (even for textures from Mojang).
• Currently, only SOCKS5 is supported.