Alternative Authentication

Alternative Authentication is a server-side mod that allows multiple third-party or custom authentication servers to coexist alongside Mojang's. By default, two providers are configured: Mojang and Ely.by. You can add, remove, or reorder them freely.

Requirements:

• online-mode=true in server.properties
• enforce-secure-profile=false is recommended, players joining via third-party providers don't have signed chat keys

Server-side only. Players using a third-party auth provider on the client need a compatible launcher or injector.

Features

• ⚙️ Configurable list of authentication providers.
• 🔐 Sequential provider fallback when a player joins the server
• 🔒 Optional fallback prevention: if a username exists on a provider but authentication fails, further providers are not tried.
• 👕 Player texture support (skin and cape) via third-party skin servers
• 📝 Whitelist support across all configured providers

How It Works

Joining the Server

When a player connects, each configured provider is tried in order until one successfully authenticates the session. If no provider succeeds, the player is denied access.

If preventFallbackIfPlayerExists is enabled and a player's username is found on a provider but authentication fails, no further providers are attempted. This prevents a user registered on a fallback service from impersonating an account on an earlier provider.

Whitelist

When a player is added to the whitelist, each provider is queried in order until the username is resolved to a UUID. If the player is not found on any provider, they cannot be added. The order in which providers are checked is determined by the providers list in the config.

What if two players share the same username across providers?

By default, the first provider to resolve the username wins. If you need to whitelist a player whose username exists on a non-primary provider, temporarily reorder the providers list and add them manually with /whitelist add.

Configuration

The config file is created automatically at config/alternative-auth.json on first launch.

configVersion

The internal schema version. Managed automatically by the mod, do not edit this manually.

debugMode

When true, detailed logs are written to the console during authentication and whitelist operations. Useful for troubleshooting. Disabled by default.

preventFallbackIfPlayerExists

When true, stops the provider chain if a username is found on the current provider but authentication fails. Prevents username spoofing via fallback services, non-premium players with usernames unique to a fallback service are not affected. Disabled by default.

providers

The ordered list of authentication providers. Each entry supports the following fields:

Field	Required	Description
name	✅	Display name for the provider
checkUrl	✅	Session validation endpoint, queried when a player joins the server
profileUrl	✅	Single username to UUID lookup endpoint, used for whitelist operations
profilesUrl	✅	Batch username to UUID lookup endpoint
propertyUrl	❌	Endpoint for fetching player properties such as skin and cape. Use {0} for the player's username and {1} for their UUID

{
    "configVersion": 1,
    "debugMode": false,
    "preventFallbackIfPlayerExists": false,
    "providers": [
        {
            "name": "Mojang",
            "checkUrl": "https://sessionserver.mojang.com/session/minecraft/hasJoined",
            "profileUrl": "https://api.minecraftservices.com/minecraft/profile/lookup/name/",
            "profilesUrl": "https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname"
        },
        {
            "name": "Ely.by",
            "checkUrl": "https://authserver.ely.by/session/hasJoined",
            "profileUrl": "https://authserver.ely.by/api/users/profiles/minecraft/",
            "profilesUrl": "https://authserver.ely.by/api/profiles/minecraft",
            "propertyUrl": "http://skinsystem.ely.by/textures/signed/{0}"
        }
    ]
}

FAQ

Q: Can't join the server, "Invalid signature for profile public key"

A: Install No Chat Reports on your server. Installing it on the client is recommended but not required.

Q: Is Forge or NeoForge supported?

A: NeoForge support is planned.

Q: When will the mod be updated to the latest Minecraft version?

A: The mod targets the latest stable release and is updated as time allows. Snapshot support is not planned.

Q: I found a bug, have a suggestion, or the mod isn't working correctly

A: Feel free to open an issue on GitHub!