For those unaware: Office 365 GCC uses Azure AD Public. For an explanation of this, please review the following:
FAQ: Why does Office 365 GCC use Azure AD Public?
”The first Office 365 US Government environment, Government Community Cloud (GCC), was created when Microsoft had a single cloud directory. The Office 365 GCC environment was designed to use Azure AD Public while still adhering to controls and requirements outlined in FedRAMP Moderate, CJIS (Criminal Justice Information Services), IRS 1075, and National Institute of Standards and Technology (NIST) publication 800-171. Azure Government, with its Azure AD infrastructure was created later. By that time, GCC had already secured the necessary compliance certifications (for example, FedRAMP Moderate and CJIS) to meet Federal, State, and Local government requirements while serving hundreds of thousands of customers. Now, many Office 365 GCC customers have two Azure AD tenants: one from the Azure AD subscription that supports Office 365 GCC and the other from their Azure Government subscription with identities in both.
Read more here:
- DOCS: Planning identity for Azure Government applications
https://docs.microsoft.com/en-us/azure/azure-government/documentation-government-plan-identity#frequently-asked-questions
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