Form Builder, CORS policy and IG Rest API

Hi,

I am working with the IG Rest API to start reviews from a workflow, and I can do that just fine using the REST activities of the workflow, where I am able to both obtain an OAuth token from my sign-on handler and communicate data to the IG Rest API. 

My issue is, that I would like to make these requests (and others) before the form is submitted, i.e. from the form itself, but whenever I attempt to send requests from the forms I run into a CORS policy block. 

Attempting to get the OAuth token:

"Access to XMLHttpRequest at 'https://<server>:8543/osp/a/idm/auth/oauth2/token' from origin 'https://<server>:8600' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource."

Attempting to reach the IG Rest API:

"Access to XMLHttpRequest at 'https://<server>:8543/api/review/reviewingTargets' from origin 'https://<server>:8600' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource."

I believe that these endpoints must allow traffic from the Form Builder origin, but is this at all possible to configure? Is there perhaps another way to make service calls which circumvents this issue?

I'd appreciate any input. Thank you for your time.