When I try querying extensionAttribute with Graph API (Hybrid Exchange), I cannot get any value.
E.g., if I try: https://graph.microsoft.com/v1.0/users/<userid or upn>?$select=extensionAttribute2, I cannot see the value even I know it’s there.
Do you know how to get it properly (or a workaround)?
Thank you
Are these values synced to Azure Active Directory? All properties for the AAD User can be found in the Microsoft Graph API docs here : https://learn.microsoft.com/en-us/graph/api/resources/user?view=graph-rest-1.0
It sounds like these are being synced from an AAD Connect environment, so it's most likely you are trying to get the onPremisesExtensionAttributes.
Per the description:
Contains extensionAttributes 1-15 for the user. Note that the individual extension attributes are neither selectable nor filterable. For an onPremisesSyncEnabled user, this set of properties is mastered on-premises and is read-only. For a cloud-only user (where onPremisesSyncEnabled is false), these properties may be set during creation or update.
I suggest taking a look more thoroughly through the documentation in regards to this. In addition to that, as you mentioned Exchange, note that the custom attributes from exchange are the same as the extension attributes. For more info on this see : https://github.com/microsoftgraph/microsoft-graph-docs/issues/5950
This is a separate sort of "Extension Attribute" but I figured I would include this in the answer as well. There is a different extensibility section for the Microsoft Graph, and the docs on this can be found here : https://learn.microsoft.com/en-us/graph/extensibility-overview
If you see information on these extensions, know that this is separate from the on-prem extensions.