I must clarify - we are the LineAct website builder, so all of our clients are
using our website builder to create and maintain their sites.

>Those links are external to the customer's site. 
Yes, we made them external, because now we using S3 for client files storage.

> Shouldn't they stay external and not mirrored at all? 
Our website builder provide unique feature - "create website archive". So
client can have a ZIP-copy of his website anytime. Clients love this feature.

> Do you have authorization to copy and distribute those resources?Of course,
because all of these files are client's own files. So client can do anything
with them, for example create their archive.