When subscribing to Microsoft Graph API events you have two options

• Regular subscription - A regular subscription event provides information on the resource type affected and the resource id, leaving it up to you to query for the resource details.
• Subscription with included properties, aka. Rich Notifications - Rich Notification subscription contain selected (defined by you) properties of the affected resource (e.g. the subject of a mail message). This event payload is encrypted with a one-time symmetric key, that in turn is encrypted with a public certificate you provided when creating the subscription.

This custom code component (no external libraries used) allows easy decryption of the rich notification payload. In addition it validates the data payload (can be skipped) to mitigate tampered payload.