Identity tokens vs Access tokens: understanding the key differences

Two token types predominate modern systems:

• Identity tokens (commonly referred to as “ID tokens” in OpenID Connect or OIDC)
• Access tokens

These types might look similar —they’re often encoded as JSON Web Tokens (JWTs)—but each serves a distinctly different purpose. ‍

Properly separating identity tokens and access tokens is critical for building secure, standards-compliant authentication and authorization flows.

What Is an Identity token?

Identity tokens confirm the user’s identity and carry user-centric data (e.g., “who” the user is, how and when they authenticated).

In an OIDC flow, the identity token is returned to your client application (such as a single-page app or mobile client) once the user has successfully logged in.

An identity token:

• Contains user details: Basic claims about the user, such as a unique ID (sub), email, or name.
• Contains an explicit audience: Your application is typically the intended audience (“this client needs the user’s information”).
• Is not meant for resource authorization: Identity tokens don’t typically manage resource access or privileges.

For a deeper dive into general authentication-token structure and usage, see “What Is an Authentication Token?”. That article provides a high-level overview of tokens, including how they’re generated, secured, and stored.

Common uses

• Showing user info: The client can decode the identity token to display “Welcome, Alice” or fetch the user’s profile picture.
• Session management: Your frontend may treat the presence of a valid identity token as proof that a user is logged in and track whether it’s expired.

What Is an Access token?

Access tokens are primarily about authorization—what the user (or calling service) can do, such as reading or updating certain data on a backend API.

In many OAuth 2.0 workflows, the authorization server returns this token, and the client sends it along with requests to protected resources.

Access tokens typically contain:

• Permissions or scopes: May include claims like scope (“read:users”, “write:profile”) or roles.
• Audience: One or more APIs or resource servers that expect this token in an HTTP header (e.g. Authorization: Bearer ...).
• Short-lived expiration dates: They often expire quickly to reduce the risk of theft. If you follow best practices, you can pair it with a refresh token for renewed access.

If you’d like to see how JWT-based tokens (including those used for resource access) are structured and validated, check out “What Are JSON Web Tokens (JWT) Used For?”.

For a hands-on look at verifying JWTs using popular libraries (Node, Go, Python, etc.), see “JWT Validation: How-to and Best Libraries to Use.”‍

Common uses

• API calls: An access token is added to API requests so the resource server can check what the user is allowed to do.
• Fine-grained permissions: Token claims or scopes can be used to limit certain endpoints to only admins or only “read” operations, etc.

Key differences

Below is a quick comparison chart of how identity tokens and access tokens differ in practice:

Why you shouldn’t mix them up

• Security clarity: An identity token is not designed to convey authorization data. Using it as a “pass” for protected resources can expose you to security holes.
• Proper audience: An ID token is intended for the client application to “know who logged in,” while an access token is specifically intended for resource servers. Mixing them can break best practices around token validation and signature checks.

Best practices for security tokens

1. Use identity tokens to personalize: Display user profile info or handle application-level session logic.
2. Use access tokens to call APIs: Scope them carefully so your APIs only allow the intended actions.
3. Validate tokens properly: Clients and resource servers should each validate the signatures and expiration of the tokens they receive (see “JWT Validation: how-to and best libraries to use”).
4. Keep tokens short-lived: Long-lived tokens can become dangerous if leaked; refresh tokens let users renew access without re-login.

Bringing it all together

In a standard OIDC+OAuth2 flow, the user logs in via your identity provider (IdP). After successful authentication, your application typically receives two tokens:

1. Identity Token – so you know who the user is within your frontend.
2. Access Token – so you can call APIs that require authorization checks.

Each token has a unique role. By separating these concerns, you preserve a clearer security boundary—your frontend uses identity tokens for session logic, and your backend (or any resource server) trusts only the access token to handle resource-level permissions.

For a broader overview of authentication tokens in general (including refresh tokens and session handling), take a look at “What Is an Authentication Token?”.

If you need a deeper look at JSON Web Tokens specifically, “What Are JSON Web Tokens (JWT) Used For?” is an excellent primer, and “JWT Validation: how-to and best libraries to use” shows you how to verify them securely.