Active Directory Authentication Library (ADAL) is a client library that lets applications acquire tokens for Azure AD and related Microsoft identity services instead of handling passwords directly. It redirects or brokers sign-in, receives an access token or refresh token, and passes that token to the application. Monitor token handling and migration to newer libraries where required.
What ADAL is doing when it acquires a token
ADAL sits between the application and Microsoft identity services. The app asks ADAL to get a token, ADAL handles the sign-in flow, and the identity service returns an access token or refresh token that the app can present when calling downstream resources. That design keeps password handling out of the application and makes token-based access the normal pattern.
In practice, the important shift is that the application is no longer “logging in” with a password each time. It is asking a client library to obtain a short-lived credential that represents the authenticated session and the permissions granted to that app. That is why ADAL is best understood as an authentication and token broker, not as a user directory or a password store.
Where ADAL fits in Microsoft identity flows
ADAL was built for the older Azure AD and Microsoft identity model, where applications commonly used redirect-based sign-in or brokered sign-in to establish trust and then reused tokens for API calls. It was widely used by desktop, web, and mobile applications that needed to call Microsoft services without building the full protocol exchange themselves.
The useful mental model is that ADAL abstracts OAuth-style token acquisition for the application developer. The app still needs a valid identity configuration, redirect URI or broker path where relevant, and a clear understanding of which resource it wants to access. For a current practitioner view of how modern token-based sign-in is structured, compare that older model with the OAuth 2.0 and OpenID Connect Guide for Identity Teams.
Because ADAL is tied to a legacy generation of Microsoft identity tooling, the practical question is usually not “how does it work?” but “what still depends on it, and what should move to newer libraries?” That matters because the protocol pattern may remain familiar while the implementation surface, support expectations, and migration path change over time.
What to watch when applications still depend on ADAL
ADAL introduces risk when token handling is poorly controlled, because the library becomes the place where access and refresh tokens are obtained, cached, and reused. If those tokens are exposed, mishandled, or kept longer than necessary, the security boundary shifts from password protection to token protection. That is why token lifecycle, storage, and retirement are the real operational concerns.
Older identity integrations also tend to accumulate technical debt. Applications may keep using legacy sign-in flows, stale configuration, or older assumptions about user prompts and broker behavior. Over time, that can complicate least-privilege design, incident response, and migration to newer identity SDKs and controls. A useful hardening reference point for legacy and modern Microsoft identity patterns is the Active Directory and Entra ID Hardening Guide.
Where ADAL is still present in production, the common failure mode is not protocol failure but lifecycle drift: tokens remain valid in places they should not, apps keep relying on legacy auth paths, and administrators lose sight of which components still depend on the old library. That makes inventory and migration planning as important as the sign-in flow itself.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-63 and NIST SP 800-53 Rev 5 set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-63 | Digital Identity Guidelines | ADAL acquires and uses digital tokens for sign-in and session access. |
| Recommendation — Use modern assurance and token guidance when replacing legacy ADAL flows. | ||
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | ADAL token handling depends on secure lifecycle control for credentials and tokens. |
| IA-2 — Identification and Authentication (Organizational Users) | ADAL mediates user sign-in for applications accessing Microsoft identity services. | |
| AC-6 — Least Privilege | Token scopes from ADAL should be limited to only the access the app needs. | |
| Recommendation — Apply IA-5 to control token issuance, storage, rotation, and revocation. Enforce strong user authentication before ADAL grants access tokens. Restrict granted token scopes to the minimum required privileges. | ||
| ISO/IEC 27001:2022 | A.5.15 — Access control | ADAL token-based access is governed through access-control policy and enforcement. |
| Recommendation — Define and enforce access-control rules for token-based application access. | ||
Practitioner Guidance
What to verify: Confirm which applications still call ADAL, which resources they access, and whether they store access or refresh tokens in a way that matches your current security requirements. If the app can be moved to a newer library, treat that as an exposure-reduction task, not just a code upgrade.
Decision rule: If the app is still functioning through ADAL but has a supported migration path, prioritise replacement before expanding the integration further. If you must keep it temporarily, constrain token scope, review token persistence, and document the dependency so it does not become invisible technical debt.
What practitioners underestimate: The library is only one part of the control surface. The real risk often sits in the token cache, session lifetime, and downstream services that trust the token without additional guardrails.
Practitioner takeaway: Treat ADAL as a legacy token-acquisition layer whose security value depends less on the login prompt and more on how tightly the resulting tokens are bounded, stored, and eventually retired.
Related resources from NHI Mgmt Group
- Active Directory Authentication Library (ADAL)
- Why is it crucial to adopt new authentication methods in MCP usage?
- How should organisations evaluate an Active Directory replacement for hybrid work?
- How should security teams govern authentication in hybrid Active Directory and cloud identity environments?