GovCloud Migration: External Accounts for JSM

[Jalesa Rogers]

We currently operate a Jira Service Management Cloud project with a public-facing customer portal used by multiple external government agencies.

Today, external users can access the portal using portal-only customer accounts (email-based accounts outside our organization). Some users may self-register or be invited as customers.

We are evaluating Atlassian Government Cloud and are trying to understand the impact of the documented restriction around “external customer accounts” not being supported.

Our questions are:

Does GovCloud completely prohibit JSM portal access for users outside the organization, or only unmanaged/self-service portal-only accounts?
Can external agency users still access JSM if they are:
provisioned manually,
federated through SSO/SAML,
or managed through Atlassian Guard / enterprise identity controls?
Has anyone successfully migrated a multi-agency/public-sector JSM portal from commercial cloud to GovCloud?
What architectural patterns are recommended for supporting cross-agency collaboration while remaining compliant in GovCloud?
If portal-only accounts are not supported, what is the recommended replacement model for external requesters?
We are specifically trying to determine whether our existing multi-agency service portal model is compatible with GovCloud, or whether we would need to redesign identity and customer access workflows.

Any real-world implementation experience would be appreciated.