Login and Auth Plugins
This page explains how Connect changes the login flow on your proxy, which login plugins conflict with it, and how to tell in advance whether a given plugin will work.
How Connect Changes Login
For players using Connect's normal authenticated flow, Connect authenticates them at the Connect edge before they ever reach your proxy or server. By the time the connection arrives at your connector, the Mojang session has already been verified and consumed. This page's UUID and skin guidance applies to those players; unauthenticated players allowed through with allow-offline-mode-players do not have a Mojang identity for Connect to supply.
For an authenticated Connect player, the Connect plugin therefore does two things during login:
- at pre-login, it marks the connection offline mode, so your proxy does not send an encryption request
- it supplies the player's real Mojang UUID and skin properties itself, out of band
This is not the same as running an offline-mode server. The player is authenticated - just somewhere else. There is no second Mojang session left for your proxy to verify, so a Connect-tunneled connection will hang if an online-mode decision reaches the proxy. The player gets no kick message and never finishes joining. Connect v0.13.1 and newer protect the documented LibreLogin path by default; arbitrary-plugin guarantees depend on proxy ordering support.
LibreLogin with Premium Autologin
LibreLogin's premium autologin handler can overwrite Connect's offline-mode decision and force the connection online. On Connect versions before v0.13.1, the proxy then sends an encryption request into a tunnel whose real client is attached to the Connect edge, and the login never completes.
LibreLogin works out of the box with Connect v0.13.1 or newer. Connect now re-asserts its own offline-mode decision after other login plugins have run, so premium autologin stays enabled and the login completes. On Velocity, Connect also restores the player's skin properties by default while leaving LibreLogin's database UUID unchanged.
On BungeeCord, the login and premium autologin fix still applies. During pre-login, BungeeCord exposes no profile-properties API on the pending connection, so restore-full-profile can re-assert the Mojang UUID and username but cannot restore skin properties through this setting.
Re-assert Configuration
The shipped defaults are:
login-reassert:
enabled: true
restore-full-profile: falselogin-reassert.enabled is the optional off-switch. Set it to false only if you deliberately want another plugin to change Connect's login decision after Connect. This restores the previous last-writer-wins behavior; a plugin that forces online mode can make Connect players hang during login again.
By default, Connect preserves the UUID chosen by the login plugin. This keeps the plugin's database lookups consistent, but code that calls Connect's isConnectPlayer(uuid) or getPlayer(uuid) API may not recognise the player under that different UUID.
To restore Connect's full profile, including the Mojang UUID and username, set login-reassert.restore-full-profile to true. Before enabling it with LibreLogin, set new-uuid-creator: MOJANG in LibreLogin's config. With LibreLogin's default CRACKED UUID creator, full-profile restoration makes its database lookups miss and its join handlers fail.
The General Rule for Any Login Plugin
The conflict is not specific to one plugin. Check any login or auth plugin against this rule:
Connect v0.13.1+ guarantees the LibreLogin path described above. For arbitrary login plugins, strict after-all protection on Velocity requires the numeric-priority API; on legacy Velocity, Connect uses PostOrder.LAST, so another LAST handler can still run after it depending on plugin load order.
| Plugin behavior | Result with Connect |
|---|---|
| Only acts on offline-mode connections, never forces online mode | Compatible by design |
| Can force online mode at pre-login | Connect v0.13.1+ re-asserts its offline-mode decision by default; on legacy Velocity, arbitrary plugins may still depend on plugin load order; older versions, or a disabled re-assert, can hang during login |
| Rewrites the game profile after Connect has set it | Connect v0.13.1+ restores skin properties on Velocity by default; the plugin's UUID remains unless full-profile restoration is enabled |
If a plugin exposes a Floodgate-style "skip externally authenticated players" exemption, its author can cooperate with Connect by including Connect's connect-player connection marker in that exemption, alongside the Floodgate one. That requires no dependency on Connect classes.
See the Compatibility Matrix for the wider set of proxy and login plugin combinations that need extra care.