Just a wild guess. But what I notice is that the your function retrieveByToken isn't using the same arguments as the interface.

Have you tried to replace

public function retrieveByToken()
  {
    return true;
  }

With this?

public function retrieveByToken($identifier, $token)
  {
    return true;
  }

After replacing with what you suggested above I get...

Declaration of Project\Providers\AuthUserProvider::updateRememberToken() must be compatible with Illuminate\Auth\UserProviderInterface::updateRememberToken(Illuminate\Auth\UserInterface $user, $token)

I got it working don't know how but all I did erased the last function and retyped everything... whitespace somewhere i don't know... I'm so lost but :) its working now.