Access tokens vs ID tokens: what IAM teams need to know

At a glance

What this is: This is a token-architecture explainer that distinguishes access tokens from ID tokens and shows how their purpose, claims, and lifespan differ in OAuth 2.0 and OIDC flows.

Why it matters: It matters because IAM teams need to align token usage with authentication, authorization, and session governance, especially when human and non-human access patterns intersect.

By the numbers:

• Microsoft access tokens are assigned random lifespans by default, ranging from 60 to 90 minutes and averaging 75 minutes.

👉 Read Descope's explanation of access tokens, ID tokens, and refresh tokens

Context

Access token and ID token design sits at the centre of modern IAM because each token carries a different security meaning. Access tokens authorise API or resource access, while ID tokens assert who the user is. When teams blur that distinction, they create weak boundaries between authentication, authorisation, and session handling.

For IAM, IGA, and application security teams, the issue is not just terminology. Token misuse can leak privilege into the wrong layer of the stack, especially when refresh tokens extend sessions and when OIDC and OAuth 2.0 are implemented without clear control ownership.

Key questions

Q: How should security teams decide when to use access tokens versus ID tokens?

A: Use access tokens when the application needs to authorise an API call or resource action, and use ID tokens when the client needs proof that authentication succeeded for a specific subject. The key decision is purpose. If a token is being used to grant access, it must be treated as an access token and validated accordingly.

Q: Why do access and ID tokens get confused in IAM implementations?

A: They get confused because both are often issued in the same login flow and both may be JWTs with similar claims. The difference is not format but meaning. Access tokens carry permission context, while ID tokens carry identity assertions. Misusing either one breaks the separation between authentication and authorisation.

Q: What breaks when applications accept the wrong token type?

A: When an application accepts an ID token as if it were an access token, it can authorise a user based on identity proof instead of entitlement. That collapses the trust boundary between login and access control. The result is over-permissioned sessions, weaker auditability, and a higher chance of privilege misuse.

Q: When should organisations revoke refresh tokens aggressively?

A: Aggressive revocation is appropriate when an employee leaves, a vendor is breached, or a token shows anomalous behaviour that suggests replay or exfiltration. The key is knowing which tokens map to which resources so revocation is targeted, not a blunt disruption event.

Technical breakdown

Access tokens in OAuth 2.0 authorise resource use

Access tokens are presented to APIs or resource servers to prove that the caller is allowed to perform an action. In practice, they are usually short-lived JWTs or opaque strings that encode scopes, issuer, subject, expiry, and issue time. Their value is in constrained authorisation, not identity proof. If an access token is replayed or over-scoped, the token becomes a bearer credential with direct operational reach.

Practical implication: keep access tokens tightly scoped, short-lived, and tied to the minimum resource set needed for the session.

ID tokens in OpenID Connect prove identity, not access

ID tokens are issued for the client application and are intended to confirm that an authentication event occurred for a specific subject. They often include claims such as audience, name, and email, along with the standard issuer, subject, expiry, and issue time fields. That makes them useful for login flows, but not for API authorisation. If an application accepts an ID token as an access decision, it confuses identity assertion with entitlement.

Practical implication: validate audience and token purpose before accepting any token as evidence of access rights.

Refresh tokens extend sessions and increase governance pressure

Refresh tokens allow a client to obtain new access tokens without forcing the user back through the full authentication flow. That improves user experience, but it also increases the importance of rotation, revocation, and exception handling. In IAM terms, refresh tokens create persistence risk if they are long-lived, reused, or insufficiently bound to the client and device context. Governance has to treat them as durable session control points, not convenience artefacts.

Practical implication: govern refresh token lifecycle with rotation, revocation, and replay detection rather than treating it as a background implementation detail.

NHI Mgmt Group analysis

Access and ID token confusion is still a control-design problem, not a terminology problem. Teams often discuss the two tokens as if the main issue were developer education, but the real issue is boundary enforcement. Access tokens are authorisation artefacts and ID tokens are identity assertions. When applications accept the wrong token type, the control plane loses the separation it depends on for least privilege and session integrity.

Token lifespan is a governance decision, not only a technical setting. A 60 to 90 minute default window may be appropriate for some human sessions, but that does not automatically map to every application, device, or delegation pattern. The governance question is whether the expiry window matches the risk of the protected resource, the revocation model, and the replay exposure. That is an IAM design choice, not a product default.

Refresh token handling is where session security becomes durable identity governance. Once refresh tokens can regenerate access tokens, the programme is no longer managing a single login event. It is managing ongoing authority across time. That changes the expectations for rotation, revocation, and anomaly detection, especially in environments where APIs, mobile clients, and delegated access all coexist.

Token purpose clarity: the cleanest control model is one where each token type is only accepted for the security function it was designed to serve. That distinction supports both modern application security and auditability. Practitioners should treat token acceptance rules as policy, not convenience.

Human IAM and non-human access patterns converge at the token boundary. The same architectural mistakes that weaken user sessions also weaken service-to-service trust when teams reuse identity patterns without re-evaluating claims, audience, and lifetimes. IAM teams that govern both human and non-human identity need a shared rule set for token purpose, not separate folklore for each stack.

From our research:

• 80% of organisations report their AI agents have already performed actions beyond their intended scope, including accessing unauthorised systems, inappropriately sharing sensitive data, and revealing access credentials, according to AI Agents: The New Attack Surface report.
• Only 52% of companies can track and audit the data their AI agents access, leaving 48% with a compliance and investigation blind spot.
• That gap is why practitioners should also study OWASP Agentic AI Top 10 as identity patterns increasingly blend human sessions, APIs, and autonomous behaviour.

What this signals

Access-token and ID-token clarity will matter even more as application stacks mix human login flows with delegated machine access. Teams that already struggle to separate authentication from authorisation will find that token misuse becomes a cross-domain governance issue, not just a developer bug.

Token purpose drift: the risk is no longer limited to one badly configured app. Once teams normalise weak token semantics, the same mistake can spread through APIs, mobile clients, and service integrations. That is why IAM programme owners should review token acceptance rules as part of architecture governance, not just incident response.

For teams mapping this topic to broader identity strategy, the relevant external anchor is NIST AI Risk Management Framework when token handling intersects with AI-driven workflows, and the practical workload-identity counterpart is Top 10 NHI Issues for machine-to-machine authentication patterns.

For practitioners

• Enforce token-type validation at every trust boundary Require applications and APIs to verify whether a presented token is an access token or an ID token before accepting it. Check audience, issuer, and intended use so identity assertions are never treated as authorisation grants.
• Tune token lifetimes to resource sensitivity Set access token expiry based on the risk of the protected resource, the expected session duration, and the revocation model. Do not rely on default windows if the application handles high-value actions or delegated access.
• Rotate and revoke refresh tokens as durable credentials Treat refresh tokens as long-lived session authority and apply rotation, revocation, and replay detection. Make sure your IAM telemetry can distinguish legitimate renewal from suspicious token reuse.
• Align OAuth and OIDC ownership across teams Document which team owns authentication flows, which team owns API authorisation, and who is responsible for token policy changes. This avoids gaps where one team assumes the other has validated token semantics.

Key takeaways

• Access tokens and ID tokens solve different problems, and confusing them weakens the security boundary between identity proof and access authorisation.
• Token lifetime, rotation, and revocation are governance choices, not just implementation details, because they determine how long authority persists.
• IAM teams should validate token purpose at runtime and govern refresh tokens as durable session credentials, not background plumbing.

Key terms

• OAuth Token: A short-lived access credential issued by an OAuth 2.0 authorisation server granting an NHI scoped access to specific resources for a defined period. Preferred over static API keys because their short lifetime limits the exploitation window if intercepted.
• Bearer Token: A bearer token is a credential that grants access to whoever possesses it, without requiring strong proof that the holder is the intended client. In NHI environments, that makes theft and replay the main risk, especially when tokens are long-lived, broadly scoped, or stored in local files.
• Refresh Token: A longer-lived credential that can mint new access tokens without forcing the user to authenticate again. Because refresh tokens can preserve access for extended periods, they are a major governance concern when malicious or over-scoped applications are granted consent.
• Token Audience: Token audience is the service or workflow a token was intended to authenticate. A valid token can still be wrong if the audience does not match the endpoint receiving it. Audience checks preserve purpose separation and stop one identity artefact from being reused across unrelated access paths.

What's in the full article

Descope's full blog covers the implementation detail this post intentionally leaves for the source:

• Field-by-field token claim examples for access tokens, ID tokens, and refresh tokens in common app flows
• Practical refresh token rotation guidance for teams building or tuning authentication journeys
• Product-oriented examples showing how token handling is implemented in a no-code identity workflow
• Context on when developers should choose OAuth 2.0, OIDC, or both in the same application

👉 Descope's full post shows the token claim differences, lifespans, and refresh token handling guidance

Deepen your knowledge

NHI governance, agentic AI identity, and machine identity lifecycle are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are responsible for identity security strategy or NHI governance in your organisation, it is worth exploring.