1) We see no way to add users programmatically, except as being added as member to a group where we only can add a mobile number. Is that correct? 2) Besides doing a bulk import via the admin interface via .csv where only mobilephone and fullname can be used, there seems an option to do a AAD sync, but we don't have it... is that because we are in Belgium? What entity in AAD is that then? User, Contact, Guest, Mail Contact, MailUser?
Conclusion: being able to manage users programmatically is really a requirement for us, but what I conclude is that the only viable option is waiting for that AAD sync to become available, or have an API call do that (but it's not there now)…
1. Currently the following ways are available to add users to groups / directory:
a. APIs to help add users via userId / Phone number.
b. Through Microsoft Flow
c. Through CSV / Excel on Management portal
d. Through the app itself
e. Through AAD sync and dynamic group creation
2. As you have rightly mentioned AAD - TUL sync is one option. However it is not available in Belgium currently (As we are live in 28 markets currently). It will be made available WW post Apr mid
3. We also have APIs to add attributes programmatically to the users. However the documentation is still not up on the docs page. If you have more queries you can send in your scenario at kaizaladev@Microsoft.com