根据apache env变量，有条件地要求HTTP身份验证

My hosting has multiple deployments of my site (dev, stage, production). How can I add HTTP Auth headers in my htaccess file if and only if the enviornment variable that they set is equal to 'dev'? (meaning they set a variable called SITE_ENVIRONMENT that can be dev, stage, or prod depending on which site you're accessing. My hosting has multiple deployments of my site