omniauth_callback_controller.rb

class OmniauthCallbackController < Devise::OmniauthCallbacksController

  def wechat
    @user = User.from_omniauth(request.env["omniauth.auth"])
    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.wechat_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end

end