Hello Teague, Kevin,
Thank you for reaching out to Microsoft Support!
Microsoft Graph is a protected web API for accessing data in Microsoft cloud services like Microsoft Entra ID and Microsoft 365. It's protected by the Microsoft identity platform, which uses OAuth access tokens to verify that an app is authorized to call Microsoft Graph.
Therefore, it cannot authenticate accounts other than Microsoft products, such as the SYS Account you mentioned.
See this document for more details.
Hope this helps.
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