When trying to access the Graph Service Client using I am receiving the error :
Code: Authorization_RequestDenied
Message: Insufficient privile
Please refer to below steps :
From your screenshot , seems you grant Read and write directory data application permission for Windows Azure Active Directory(azure ad graph api) . Since you are using microsoft graph (https://graph.microsoft.com/) , you need to grant application permission for Microsoft Graph :
Since you are admin in your AAD, You could grant permission for users in organization by click Grant permission button shown in above screenshot .
Then you could use your code (client credential flow to get the token) and query users information . If you check the claims in access token issued by azure ad , you could find Directory.Read.All permission in roles claim .