Why does Active Directory Authentication Library (ADAL) matter for security teams?

Why ADAL still matters to a security team’s inventory

ADAL is not just a legacy library, it is a dependency that can still shape how applications obtain tokens and how much control security teams have over authentication flows. If an app still uses it, that app may depend on older patterns, older consent grants, or older integration decisions that were made before current identity guidance. Tracking those dependencies is part of reducing hidden authentication debt.

For teams managing hybrid estates, the question is rarely whether ADAL works today, but whether it is still the right trust path. Legacy libraries can keep old app registrations alive longer than intended, preserve broad permissions, and make it harder to see which applications are still using the old flow versus a modern supported path. That makes ADAL a visibility and governance issue as much as a development issue.

ADAL matters because it often sits in the middle of application authentication, token acquisition, and authorisation decisions that security teams need to understand end to end. The practical task is to identify every app, service, script, and integration that still depends on it, then decide whether the dependency can be removed, isolated, or tightly reviewed before it becomes a source of drift.

That migration mindset is well aligned with the broader identity control plane guidance in the Workforce Identity Security Guide and the IAM and Identity Provider Buyer’s Guide, because both emphasise lifecycle control, sign-in standards, and reducing brittle dependencies.

What security teams should review in ADAL-dependent apps

The first review is simple inventory. Security teams need to know which applications still use ADAL, what identities they use to authenticate, which tokens they request, and whether those permissions still match current business need. In practice, that means reviewing app registrations, delegated and application permissions, service principals, and any scripts or automation that silently rely on the old library.

The second review is consent and token behaviour. Legacy authentication code can leave behind overbroad consent, long-lived access, or poorly understood refresh behaviour. That does not automatically mean compromise, but it does mean the team should verify who approved access, what scope was granted, and whether the app still needs that level of access today.

The third review is migration readiness. If an application can move to a supported library without changing business logic, do that first. If not, isolate the dependency, reduce its permissions, and put it on a visible remediation track. The point is not to preserve old integration convenience, but to remove hidden auth paths that are harder to govern and monitor.

Security teams often discover that the most important problem is not the library itself but the surrounding estate. Legacy dependencies tend to cluster with weak secret handling, stale registrations, and inconsistent ownership. That is why ADAL review should be tied to application ownership and credential hygiene, not treated as a one-off code audit.

For teams that need a practical migration lens, NHI Lifecycle Management Guide is useful for the ownership, rotation, and offboarding discipline around long-lived application dependencies, while Active Directory and Entra ID Hardening Guide helps frame how legacy identity paths fit into broader hardening priorities.

How ADAL changes migration, monitoring, and control decisions

Once ADAL is identified, the security decision is usually about priority rather than awareness. If the app touches sensitive data, production admin functions, or broad tenant permissions, migration should move up the queue. If the app is low risk but still legacy, at minimum it should be documented, constrained, and monitored so that it does not become an invisible exception.

Monitoring also changes. Security teams should not just watch for failed sign-ins or obvious abuse, but for unusual token issuance patterns, unexpected consent grants, dormant apps that suddenly become active, and sign-in activity from identities that were supposed to be retired. Those signals are especially important where legacy libraries are used by service accounts or unattended automation.

ADAL also affects incident response. If a legacy app is compromised, the team may need to review not only the application secret or certificate, but also the delegated consent trail, the token audience, and any downstream resources that app could reach. In other words, the relevant blast radius may be wider than the code owner expects.

That is why the migration conversation should be tied to operational evidence, not just developer preference. If the team cannot easily explain which apps use ADAL, what they can access, and who owns the permissions, then the dependency is already a control gap.

For current protocol guidance, the NIST SP 800-63 Digital Identity Guidelines are useful for understanding modern authentication expectations, and OpenID Connect Core 1.0 remains the clearest reference for how modern token-based sign-in should be structured around current standards rather than legacy client behaviour.

Risk and Threat Considerations

Legacy authentication libraries increase exposure when they preserve old permissions, stale secrets, or unclear consent relationships. The risk is not that ADAL is automatically malicious, but that it can anchor applications to older trust assumptions that are easier to misconfigure and harder to observe.

Failure mechanism: An application keeps using an outdated authentication path, retains broad token access, or remains tied to an overprivileged registration that was never re-reviewed after the original deployment.

Impact: Attackers or insiders who obtain the app’s token path, consent, or secret can reach more resources than intended, while defenders have less clarity about what the app is legitimately allowed to do.

Practitioner Guidance

What to prioritise: Start with apps that hold sensitive data, production access, or broad delegated permissions. Those are the cases where a legacy library creates the largest security and governance gap if it remains unreviewed.

What to verify: Confirm the owning team, the current permission set, the consent history, and whether the app still needs the same token scope. If you cannot explain those four things clearly, the dependency should be treated as an active control issue.

Common mistake: Treating ADAL removal as a pure developer refactor. In practice, it is also an identity inventory, permissions, and lifecycle exercise, especially where service or automation accounts are involved.

Practitioner takeaway: The security value is not in “using a newer library” by itself, it is in making every application’s authentication path visible, least-privileged, and supportable enough to govern confidently.

Related resources from NHI Mgmt Group

• Guide: OAuth 2.0 and OpenID Connect Guide for Identity Teams
• How should security teams govern authentication in hybrid Active Directory and cloud identity environments?
• How should security teams unify phishing-resistant authentication across Active Directory and Entra ID without creating duplicate credential workflows?
• How should security teams reduce exposure from legacy Active Directory compatibility settings without breaking authentication or Group Policy?
• How should security teams handle external Active Directory trusts when cross-domain authentication is in scope?