Setting up Cross Origin Resource Sharing (CORS) for apps is important from a security point of view but not typically understood very well. Most people likely want to avoid dealing with CORS but you need someone in your team who understands it well to set it up.

CORS is a key construct for managing secure access to your app. Resources that use Javascript which need to use other resources hosted in a different domain need to have proper permissions setup to make it work. 

Dyavanapellisujal helps explain how CORS works using a website running out of an S3 bucket.