class ActionDispatch::Routing::Mapper

def set_omniauth_path_prefix!(path_prefix) #:nodoc:
  if ::OmniAuth.config.path_prefix && ::OmniAuth.config.path_prefix != path_prefix
    raise "Wrong OmniAuth configuration. If you are getting this exception, it means that either:\n\n" \
      "1) You are manually setting OmniAuth.config.path_prefix and it doesn't match the Devise one\n" \
      "2) You are setting :omniauthable in more than one model\n" \
      "3) You changed your Devise routes/OmniAuth setting and haven't restarted your server"
  else
    ::OmniAuth.config.path_prefix = path_prefix
  end
end