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Tickwise
ErrorAuthenticationSIG-AU-001

Mojang authentication failure: the server cannot verify player sessions

Platforms
Velocity · Paper · Purpur · whole network
Verified
Verified
Confidence
Confidence 70%

What it looks like in the log

Any one of these lines is enough. The agent matches them locally, on your server.

logs/latest.log
  • whilst contacting Mojang to log in
  • [ERROR] Unable to authenticate player
  • Couldn't verify username because servers are unavailable

Symptoms

  • Premium players cannot join: “Authentication servers are down. Please try again later, sorry!”
  • The proxy log shows errors when contacting Mojang's sessionserver

Cause

The server could not verify the player's session with Mojang (sessionserver.mojang.com): the authentication service is unavailable or returning errors, or the server has no outbound access to it.

Possible causes

  • Outage or rate limiting on Mojang's session servers (5xx/429 responses)
  • No outbound access to sessionserver.mojang.com: DNS, firewall or the host's outbound rules, ISP blocking
  • authlib-injector (Ely.by and similar) is in use — check their authentication server, not Mojang's
  • noteA single error can occur during a brief outage; the cloud judges how widespread it is by the number of events

How to fixLow risk

  1. Check the status of Mojang/Microsoft services: if the outage is global, all you can do is wait for recovery — retrying the login will not help.
  2. From the proxy host, check outbound access: DNS resolution of sessionserver.mojang.com and an HTTPS connection to it (curl/wget); check the outbound firewall rules and the hosting panel.
  3. If authlib-injector (Ely.by and similar) is in use, check that their authentication server is reachable and check the -javaagent parameter in the launch command.
  4. Do not switch the proxy to online-mode = false to work around the outage: it lets anyone join under any name.

Translated from the Russian original; log lines are quoted verbatim.

Sources