SharePoint — GetXRequestDigest call is failing with 403

We are trying to connect Sharepoint online instance using SAML Authentication. We are trying to create site using Rest API. As we are using SAML authentication , we need to use /contextinfo to obtain request digest. This was working absolutely fine , but not sure why it is throwing error 403 now.

Following is the request sample :

URL: https://yourdomain.sharepoint.com/_api/contextinfo, headers: { Cookie: rtFa=xxxx;FedAuth=xxx; Origin: yourdomain.sharepoint.com }

-2147024891, System.UnauthorizedAccessExceptionAccess denied. You do not have permission to perform this action or access this resource.