UPDATE: And Steam Auth is back up, so you can now log in and being playing via Steam. Apologies for the delays in getting you playing all.
We are seeing lots of reports of players struggling to sign-in with Steam today. This is due to an issue with Steam's Authorization API which is affecting lots of other games and this is currently being investigated.
Please note this only affects users who sign into Robocraft using Steam credentials. If you use your Robocraft account details you will be unaffected by this issue.
If you have given your email to us in the past (either by registering or inputting your email in the in-game Verify your Email Prompt) you can sidestep these current Steam-only sign-in issues by inputting your email in the password reset prompt here: http://robocraftgame.com/recover-account-details.php
Follow all the steps, then proceed to sign in with your Robocraft account details and you will be able to get in game.
Apologies for this error all. When we have an update, we'll pop it in this thread.