SAS URL File Download in Groovy Business Rule

Summary:

I have an SAS URL that works to return the contents of a file when used in a browser or curl, but it fails with 403 Authentication Error when I try to use the HttpRequest get() method in a Groovy business rule in Planning.

All of the information needed is contained in the URL, so there should be no headers or body needed. I have tried with on-demand and named connections.

I suspect the EPM Connection is including something extra that is not needed (like an Authentication header) but I don't know how to tell.

Content (please ensure you mask any confidential information):