Alternative Authentication NeoForge

Alternative Authentication NeoForge is an unofficial NeoForge 1.21.1 port of Alternative Authentication, originally created by GGSkyOne.

This mod allows a Minecraft server to authenticate players using multiple authentication providers, including Mojang and third-party services such as Ely.by, without replacing or interfering with Mojang authentication.

It is designed for Minecraft 1.21.1 using NeoForge.

This is a port of the original Alternative Authentication mod. The original project targets Fabric and Quilt. This version targets NeoForge 1.21.1.

Requirements

This mod requires the server to run with:

online-mode=true

This is required for the authentication flow to work correctly.

It is also recommended to set:

enforce-secure-profile=false

This disables Mojang secure chat profile enforcement, which players using third-party authentication providers usually cannot provide.

Important notice

This is a server-side only mod.

Players do not need to install this mod on their client. However, players who want to join using a third-party authentication provider need to use a compatible launcher or an authlib-injector setup.

Microsoft/Mojang players can still join normally as long as the Mojang provider is enabled in the configuration.

Features

• ⚙️ Configurable authentication providers.
• 🔐 Support for third-party authentication servers.
• 🔁 Provider fallback when a player joins the server.
• 👕 Support for player textures from third-party skin servers.
• 🌐 Support for fetching additional player properties during login.
• 📝 Whitelist support for third-party authentication providers.
• 🧩 Ported to NeoForge 1.21.1.

Default providers

By default, the configuration includes:

• Mojang
• Ely.by

You can add, remove, or reorder providers in the configuration file.

How joining works

When a player joins the server, the mod checks the configured authentication providers in order.

By default, Mojang is checked first. If the player cannot be authenticated through Mojang, the mod then checks Ely.by or any other configured provider.

You can change the provider order in the configuration. For example, you can check Ely.by first and Mojang second.

If the player cannot be authenticated by any configured provider, they will not be allowed to join the server.

Whitelist support

This mod extends whitelist handling so that players from third-party authentication providers can be resolved and added to the whitelist.

When adding a player to the whitelist, the mod checks the configured providers in order.

If the player is found on one of the providers, their profile can be added to the whitelist.

If the player cannot be found on any provider, they cannot be added automatically.

What if the same username exists on multiple providers?

If the same username exists on multiple authentication providers, the first matching provider in the configuration order will be used.

To handle this, you can temporarily change the provider order or manually edit the whitelist entry.

Configuration

The configuration file is located at:

/config/alternative-auth.json

Example configuration:

{
    "debug": false,
    "providers": [
        {
            "name": "Mojang",
            "check_url": "https://sessionserver.mojang.com/session/minecraft/hasJoined",
            "profiles_url": "https://api.mojang.com/profiles/minecraft"
        },
        {
            "name": "Ely.by",
            "check_url": "https://authserver.ely.by/session/hasJoined",
            "profiles_url": "https://authserver.ely.by/api/profiles/minecraft",
            "property_url": "http://skinsystem.ely.by/textures/signed/{0}"
        }
    ]
}

Configuration options

debug

Enables additional logs during authentication and whitelist operations.

Default:

false

Set this to true when troubleshooting authentication issues.

providers

List of authentication providers used by the server.

Providers are checked from top to bottom.

Each provider can define the following fields:

name

Display name of the provider.

Example:

"name": "Ely.by"

check_url

URL used to verify a player when they join the server.

Example:

"check_url": "https://authserver.ely.by/session/hasJoined"

profiles_url

URL used to resolve player profiles when adding or removing players from the whitelist.

This endpoint must support checking multiple usernames using an array.

Example:

"profiles_url": "https://authserver.ely.by/api/profiles/minecraft"

property_url

Optional URL used to fetch additional player properties, such as skin and cape textures.

You can use:

• {0} for the player username
• {1} for the player UUID

Example:

"property_url": "http://skinsystem.ely.by/textures/signed/{0}"

FAQ

Is this the original mod?

No. This is an unofficial NeoForge 1.21.1 port of Alternative Authentication.

The original mod was created by GGSkyOne and is available on Modrinth.

Does this support Fabric or Quilt?

No. This port targets NeoForge 1.21.1.

Use the original Alternative Authentication mod if you need Fabric or Quilt support.

Does this support Forge?

No. This version targets NeoForge 1.21.1 only.

Is this client-side?

No. This is a server-side mod.

Players do not need to install it, but third-party authentication users need a compatible launcher or authlib-injector.

Can Mojang and Ely.by players join the same server?

Yes.

As long as both providers are configured, Mojang and Ely.by players can join the same server.

Can Microsoft/Mojang players still join?

Yes.

Mojang authentication still works normally if the Mojang provider is enabled.

Why does online-mode=true need to stay enabled?

This mod extends Minecraft’s online authentication flow instead of replacing it with offline mode.

Keeping online-mode=true allows Mojang authentication to keep working correctly while also supporting third-party providers.

Why is enforce-secure-profile=false recommended?

Third-party authentication providers usually cannot provide Mojang secure chat profiles.

Setting enforce-secure-profile=false prevents those players from being rejected because of missing signed chat data.

Credits

Original mod: Alternative Authentication Original author: GGSkyOne

This NeoForge version is an unofficial port for Minecraft 1.21.1.