That's hard for a web forum with BBCode -- posts can load external images on non-HTTPS domains. I suppose I can have the BBCode alter the URLs to point to my d

That's hard for a web forum with BBCode -- posts can load external images on non-HTTPS domains. I suppose I can have the BBCode alter the URLs to point to my domain, and use nginx to proxy the image loads. I'd have to be careful to make sure users can't proxy malicious scripts and stuff into the page (because it'd be same-origin); is there a standard solution for this?