@mhammond4
Did you wait for the provisioning report to finish and then use the URL supplied? When you make the POST, it starts the process of generating the report and gives you a progress report until it's done. Check the status of the report to see if it's ready for download.
Once the report status is "complete" and the progress is "100", then there should be an URL that you can use.
The first one says file_url, for example, the pathname may be "/accounts/1234/files/109772350/download"
That is not an API call and you have to be logged into Canvas to use it. Adding the Authorization header won't help since you're not using the API.
There is also an attachment object that has a URL. This URL with have a query string with a download_frd=1 and a verifier code on it. The verifier code is what allows you to access it without being logged into Canvas.
You have undoubtedly seen the Accounts Report API documentation or you wouldn't be as far as you are (unless you're trying to fix someone else's code), but I link it here for other people who may stumble across this question.