Redirect was blocked for CORS request.

Hi,

I have a javascript website which is communicating with a webapi2 REST api.  The entire site is authenticated through an Azure Active Directory and recently we started to get 

SEC7127: Redirect was blocked for CORS request. 

messages.  This happens after remaining connected for about 30 - 60 minutes and I assume this is because one of the API calls are being redirected to the microsoft authentication server.  How do I stop this happening?

Geoff.