MSGraph API: How to get outlook categories of other user as described in the API

Question

I am trying to get the category names/colours via the API for a user other than myself, the documentation says it is possible, see image below, but returns "Access is denied. Check credentials and try again." even though I do have permission to that mailbox.

Seem this question was also asked almost 3 years ago with no answer, guessing the API documentation describes a scenario that the developers forgot to program for???

Previous posting of the same question

Here is the full request and showing the permissions are allowed.

Answer 1

You can't do it using delegate permissions because there is no MailboxSetting.ReadWrite.Shared permission so that endpoint can only be used to access the current users Mailbox setting when using delegate permission. You an use Application Permissions and the Client Credential flow https://learn.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-client-creds-grant-flow if you need to limit the scope of your application to a number of Mailboxes you can do that as well https://learn.microsoft.com/en-us/graph/auth-limit-mailbox-access