• Create a new application in App Registration under Azure AD.
• Once the application is created copy the Object ID.
• Open Graph Explorer by using https://developer.microsoft.com/en-us/graph/graph-explorer# url.
• Click on Sign in with Microsoft on the left and Sign in with Global Admin account who is a member of same directory and not added as external (guest) user.
• In Graph Explorer, click on Modify permissions > select Directory.AccessAsUser.All > click Modify Permissions.
• Click on Accept at consent page.
• In Graph Explorer, use following query. Where, <ObjectID_of_the_application> is the value copied in Step 2.

POST https://graph.microsoft.com/beta/<your_tenant.onmicrosoft.com>/applications/<ObjectID_of_the_application>/extensionProperties

• Use following text in the Request body. Since the targetObject is user, the attribute will be created for all Users in the tenant. Note: Please type the request body manually as with copy-paste Graph Explorer will not recognize some of the characters.

{
"name": "employeeType",
"dataType": "String",
"targetObjects": ["User"]
}

• To update the attribute with a value use:

Call:
PATCH https://graph.microsoft.com/beta/users/your_globaladmin@your_tenant.onmicrosoft.com
Body:{"extension_e175b1fc21b144019cadxxxxxxxxxxxx_employeeType":"Value_to_be_assigned"}

• To verify if the attribute is updated successfully run following query:

GET https://graph.microsoft.com/beta/users/<User’s_UPN_or_Object ID>