Hi,
Finally my problem is solved, thanks to zzomp from the DELL Community.
The authentication failed because of my NPS server which is still under Windows Server 2012R2, that uses TLS 1.0 and 1.1 but not 1.2
The ThinOS 2303+ documentation reveals that point :
To further improve the security of ThinOS devices, TLS 1.0 and 1.1 have been removed in ThinOS 2303. If your network or
VDI environments still require TLS 1.0 or 1.1, use ThinOS 2211 or earlier versions until you have updated your environment.
So I had to activate TLS 1.2 by simply adding a registry key to the NPS server :
https://community.spiceworks.com/topic/2195158-enable-tls1-2-in-windows-server-nps
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\13]
“TlsVersion”=dword:00000c00
Then restart the EAP service, and that’s it ! authentication passed !