Driver loading in Windows 10 safe mode

Hello,

What is the requirement for a driver to keep working in Windows 10 safe mode? It says the driver is not signed, the driver is attested with certificate from Microsoft but not WHQLed. The driver does load in normal boot and work as expected with signature from Microsoft. The end customer wants the driver to be working in safe boot as well.

Has anyone gotten any idea?

Thanks,
Hasan