We published a sample app on GitHub to walk you through authentication to Microsoft Graph - both User-delegated auth and Application-only auth.
This will help you better understand the auth tokens and their contents, and debug potential issues you may encounter.
The sample application displays the internals both of the auth token (User-delegated or App-only) and the response to the query submitted to the Microsoft Graph Security API as shown below.
Enjoy!
The Microsoft Graph Security API Team