unless 后面的代码： &后面加上一个点是什么意思？

def create
   @user = User.find_by_email(user_params[:email])
   unless @user&.authenticate(user_params[:password])
     head 401 
     return
   end

   payload = {user_id: @user.id}
   exp_time = 24.hours.from_now
   if (JsonWebToken rescue nil) 
     token = JsonWebToken.encode(payload, exp_time) 
     render json: {error_code:0, data:{token:token, exp_time:exp_time}, message:"ok"}, status: 201
     return
   else
     head 401
   end
end

 private
   def user_params
     params.require(:user).permit(:email, :password)
   end