I have an on-premises Windows server 2022, which is running AD DS, NPS and DHCP. I also have Azure AD subscription, where my users are located. I would like to keep my users database (AD) in the cloud, since currently, I do not have any backup solutions and it is easier for me to manage. I want to have ieee 801.x on premises, as well as VPN service. Is it possible to force the NPS to authenticate against the Azure AD, where all my users are located? If yes, how can this be done?
I know that Azure AD Connect provides hybrid integration, but from what I read, it is only one way, i.e from on-premises AD to cloud synchronization, but not the other way around.
Yes, you are correct that the synchronization is only one-way and the workarounds currently are to use use PowerShell export/import or use a third-party tool. In the NPS article you linked, the on-premises users ultimately authenticate against Azure MFA. The NPS extension acts as an adapter between RADIUS and cloud-based Azure AD Multi-Factor Authentication to provide MFA for the federated or synced users. Your cloud users would just use regular Azure MFA without needing that adapter.
The most common workaround for the user writeback scenario is to create a PowerShell script that scans Azure AD regularly, finds the users in Azure, and then creates an on-premises user with the attributes in Azure AD.
The regular user writeback feature is on the roadmap and actively being worked on though. I've asked for an update from the PG and will edit this post once it is available.
For cloud VPN options, see: Azure AD Authentication - Open VPN.