What should IAM leaders do when an identity provider must remain in place during migration?

Treat it as a temporary trust boundary with documented expiry conditions, not a permanent exception. Restrict new dependencies, keep application mappings explicit, and track which access flows still rely on the older provider. If the coexistence state has no end date, it becomes inherited sprawl rather than migration support.

Why This Matters for Security Teams

Keeping an identity provider alive during migration is not just a technical coexistence choice. It creates a second trust boundary, and every extra trust boundary increases the chance that access paths, application mappings, and approval logic drift out of sync. NIST’s NIST Cybersecurity Framework 2.0 treats identity governance as part of resilient risk management, which is the right lens here: the older provider must be managed as a bounded exception, not a default operating model.

This matters because migration periods are where hidden dependencies accumulate. Teams often preserve legacy access to avoid outages, then discover that the “temporary” provider still fronts applications, service accounts, and automation long after the cutover plan was supposed to end. NHIMG’s Ultimate Guide to NHIs explains why non-human access becomes risky when the identity layer is allowed to grow without explicit lifecycle controls. In practice, many security teams encounter access sprawl only after applications have already been reattached to the old provider, rather than through intentional migration governance.

How It Works in Practice

The practical answer is to treat coexistence like a controlled transition state with an owner, expiry conditions, and a measurable exit path. The older identity provider should be allowed only where a specific application, integration, or access flow still depends on it. New workloads should not be onboarded to the legacy provider unless there is a documented exception, and that exception should carry a date, a remediation plan, and a named approver.

For IAM leaders, the migration model usually works best when three things happen together:

• Application-to-provider mappings are inventory-backed and reviewed continuously, not assumed from architecture diagrams.
• Access rules are explicit per application, service account, or workload, so coexistence does not become a silent shared trust layer.
• Cutover criteria include telemetry, so teams can see which authentication flows, tokens, or provisioning jobs still rely on the old provider.

This is especially important for non-human identities, where the impact is often larger than for user sign-in. The 2024 Non-Human Identity Security Report found that 88.5% of organisations say their NHI practices lag behind or merely match human IAM, and 35.6% cite consistent access across hybrid and multi-cloud environments as their top challenge. That mismatch is a warning sign: if migration planning does not include workload identities, service principals, API keys, and automation paths, the legacy provider can remain embedded in infrastructure long after the business thinks the migration is complete. NIST guidance on digital identity and identity assurance also supports a bounded, auditable transition rather than indefinite dual operation, and that approach aligns well with NIST Cybersecurity Framework 2.0 governance expectations.

These controls tend to break down when the legacy provider is still required for unmanaged third-party integrations, because no one owns the dependency removal work end to end.

Common Variations and Edge Cases

Tighter coexistence control often increases migration overhead, requiring organisations to balance continuity against operational drag. That tradeoff is real, especially when directory sync, federation, or vendor-hosted applications cannot move on the same timeline as internal systems. Current guidance suggests the key is not to eliminate the old provider instantly, but to prevent it from becoming an untracked permanent exception.

One common edge case is split ownership: infrastructure teams may run the migration mechanics while application owners control the actual authentication dependencies. Another is “read-only legacy,” where a provider is kept alive only for verification or fallback. That can be acceptable, but only if its scope is narrowed and its use is observable. If the old provider still issues credentials, performs provisioning, or acts as the source of record for access rights, the migration is not really in a coexistence phase anymore.

Another nuance is that some environments need a longer tail for regulated or embedded systems. Best practice is evolving here, and there is no universal standard for how long coexistence may last. What matters is that the expiry condition is concrete: specific applications moved, specific flows retired, specific identities rehomed. NHIMG’s Top 10 NHI Issues is useful context for spotting where hidden non-human dependencies linger, while 52 NHI Breaches Analysis shows how control gaps tend to appear when identity exceptions outlive their intended purpose.

If the coexistence state has no end date, no dependency register, and no enforced decommission path, it should be treated as identity sprawl, not migration support.

Related resources from NHI Mgmt Group

• How should IAM teams interpret developer summit content for identity governance?
• What should IAM teams do when identity services are part of a public-sector supply chain?
• Who is accountable when a government identity control fails during an incident?
• What breaks when policy parity is incomplete during endpoint migration?