Decide which legacy flows will be retired, which will be time-limited, and which will be prohibited entirely. Then align security, support, and product ownership so the default journey favours passkeys and the exception paths do not reintroduce phishable access.
Retiring, Limiting, and Banning Legacy Password Flows
When passkeys land in an environment that still supports passwords, the hard part is not the cryptography, it is the transition design. Identity teams need an explicit policy for each legacy path: retire it where possible, time-limit it where migration is incomplete, and prohibit it where it would keep a phishable recovery path alive. The Passwordless and Passkeys Guide is a practical reference for making that rollout decision.
That policy should also account for the support burden created by partial migrations. If the password path remains easier than the passkey path, users and help desks will drift back to the old flow during account recovery, device replacement, or enrolment failure. The safer default is to make passkeys the normal journey and reserve legacy authentication for narrowly defined exception handling.
Why Coexistence Fails When the Exception Becomes the Default
Coexistence usually breaks when organisations keep the old workflow as a universal fallback instead of a controlled exception. A password-era path can quietly undermine passkeys if it still allows password reset, SMS-based recovery, or help-desk override without strong proof of possession. The result is not just weaker authentication, it is a second route around the protections passkeys were meant to provide. Workforce Identity Security Guide ties this problem to phishing-resistant sign-in, recovery handling, and session theft.
Teams also need to watch for policy drift across product, security, and support. A product team may preserve an old login for convenience, support may keep a manual reset path for speed, and security may assume the passkey policy is already enforced. Those independent choices add up to a brittle mixed estate where the strongest authentication method is present, but not decisive.
How to Set the Default Journey Without Breaking Operations
The practical goal is to make the passkey path the shortest, clearest, and most strongly supported route. That means onboarding, reauthentication, and recovery should all point users toward passkeys first, while passwords become temporary, constrained, and visible exceptions. If a legacy flow must remain, it should have a clear expiry date, explicit owner, and a removal trigger tied to adoption or risk.
It also helps to distinguish between account access and account recovery. A passkey can secure routine sign-in while a separate recovery policy handles lost devices, lost authenticators, or first-time enrolment. If recovery still depends on easily phishable factors, the environment has not really left the password era, it has just renamed it. For a broader comparison of methods and rollout trade-offs, the MFA Guide remains useful.
Risk and Threat Considerations
Mixed passkey and password workflows create a residual attack surface even when the new method is sound. The most common failure is not passkey bypass, but the survival of one weak fallback path that attackers can target through phishing, help-desk social engineering, or account recovery abuse.
Failure mechanism: An organisation keeps password reset, SMS recovery, or manual support override active after passkeys are deployed, so an attacker only needs the weaker path once to regain durable access.
Impact: Compromise of the legacy path can nullify the security benefit of passkeys, enable account takeover, and create a false sense that the account is protected by phishing-resistant authentication.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 addresses the attack and risk surface, while NIST SP 800-53 Rev 5 and NIST SP 800-63 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | Passkey coexistence hinges on legacy credential lifecycle and retirement. |
| IA-2 — Identification and Authentication (Organizational Users) | The topic is about how users authenticate during a transition to passkeys. | |
| IA-9 — Identification and Authentication (Non-Organizational Users) | Coexisting workflows often include external or contractor access paths that must be governed. | |
| Recommendation — Retire or time-limit legacy authenticators and enforce controlled replacement paths. Require phishing-resistant authentication for primary workforce sign-in. Apply stronger authentication to any non-employee access path that remains. | ||
| NIST SP 800-63 | Digital Identity Guidelines | Passkeys, authenticator assurance, and recovery design are central to the question. |
| Recommendation — Use the digital identity guidance to set assurance and recovery requirements for passkey rollout. | ||
| OWASP Non-Human Identity Top 10 | NHI-10 — Human Use of NHI | The question concerns human-access journeys that should not fall back to weaker shared or phishable paths. |
| Recommendation — Prevent human-operated fallback paths from reintroducing weak authentication. | ||
Practitioner Guidance
Decision rule: If a legacy flow can still authenticate into production, treat it as a live attack path, not a harmless backup. The right question is whether the exception is narrow, time-bound, and harder to abuse than the passkey path it replaces.
What to verify: Confirm that support teams, product owners, and identity engineers all understand which flows are retired, which expire, and which are prohibited. If you cannot name the owner of each exception path, the path is already too permissive.
What good looks like: Users can complete normal sign-in with passkeys, recovery requires stronger scrutiny than routine access, and legacy authentication is disappearing rather than accumulating as permanent debt.
Practitioner takeaway: A passkey rollout is successful only when the legacy journey becomes measurably harder to use, easier to govern, and steadily less necessary.
Related resources from NHI Mgmt Group
- When should identity teams prioritize passkeys over password resets and SMS MFA?
- Why do mobile password workflows increase governance demands for identity and credential teams?
- How should security teams authenticate AI agents in enterprise environments?
- How should security teams implement Client ID Metadata Documents?
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Reviewed and updated by the NHIMG editorial team on October 8, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org