Configure an Entrust-hosted Enrollment Gateway to operate as SCEP Server and process Intune enrollment requests with PKIaaS Certification Authorities.

See the following video for a quick guide on the required steps.

See also the Microsoft documentation for details on the third-party SCEP integration with Intune. 

https://learn.microsoft.com/en-us/mem/intune/protect/certificate-authority-add-scep-overview