Instructions for

Validate Access Tokens

This guide explains why access token validation is important and how to validate and decode the access token.

Learning outcomes

Understand token validation.
Understand what to check when validating tokens.
Decode access tokens.
Validate access tokens remotely.

About access token validation

If you're building a modern app or API, you want to know if your end user is authenticated. This is important to give context or to protect APIs from unauthenticated users. You can use Okta to authenticate your end users and issue them signed access and ID tokens. Your app can then use these tokens. It's important that your app uses only the access token to grant access, and not the ID token. See Access tokens vs ID tokens.

After signed tokens are issued to end users, they can be passed to your app for validation. There are two ways to verify a token: locally or remotely with Okta. The token is signed with a JSON Web Key (JWK) using the RS256 algorithm. To validate the signature, Okta provides your app with a public key that you can use.

To jump straight to the local validation steps: What to check when validating an access token
To see how to validate a token directly with Okta: Validate a token remotely with Okta

Note: Okta is the only app that should consume or validate access tokens from the org authorization server. Org authorization servers have the following issuer format: https://{yourOktaOrg}. Consider these access tokens as opaque strings because their content is subject to change at any time. Therefore, any attempts by your app to validate the tokens may not work in the future.

Access tokens vs ID tokens

Access tokens are intended for authorizing access to a resource. It's important that the resource server (your server-side app) accepts only an access token from a client.

ID tokens, on the other hand, are intended for authentication. They provide information about the resource owner so that you can verify that they're who they say they are. Authentication is important to clients. Because of this, when a client makes an authentication request, the ID token that's returned contains the client_id in the ID token's aud claim.

What to check when validating an access token

The high-level overview of validating an access token looks like this:

Retrieve your Okta JSON Web Keys (JWK) (opens new window), which your app should check periodically and cache.
Decode the access token, which is in JSON Web Token (JWT) (opens new window) format.
Verify the signature used to sign the access token.
Verify the claims found inside the access token.

Retrieve the JSON Web Keys

Decode and validate the access token

Decode the access token, which is in JWT format. This involves the following steps:

Verify the token signature.
Verify the claims.

This code uses the Okta JWT Verifier for Golang (opens new window).

For any access token to be valid, the following must be asserted:

Signature is valid. The private key signed the token, and this private key has a corresponding public key in the JWKS response from the authorization server.
Access token isn't expired. This requires the local system time to be in sync with Okta and checks the exp claim of the access token.
The aud claim in the JWT matches any expected aud claim passed in ClaimsToValidate during setup.
The iss claim matches the issuer that the verifier is constructed with.
Custom claim assertions that you add are confirmed.

import github.com/okta/okta-jwt-verifier-golang

toValidate := map[string]string{}
toValidate["aud"] = "api://default"
toValidate["cid"] = "{clientId}"

jwtVerifierSetup := jwtverifier.JwtVerifier{
        Issuer: "{issuer}",
        ClaimsToValidate: toValidate
}

verifier := jwtVerifierSetup.New()

token, err := verifier.VerifyAccessToken("{JWT}")

You may need to adjust your clock skew leeway. Okta defaults to a PT2M clock skew adjustment in our validation. You can adjust this to your needs by setting the SetLeeway in seconds after getting a new instance of the verifier:

jwtVerifierSetup := JwtVerifier{
        Issuer: "{issuer}",
}

verifier := jwtVerifierSetup.New()
verifier.SetLeeway(60) // seconds

Validate a token remotely with Okta

Alternatively, you can validate an access or refresh token using the Token Introspection endpoint: Introspection request (opens new window). This endpoint takes your token as a URL query parameter and returns a simple JSON response with a Boolean active property.

This involves a network request that is slower for performing validation. But, you can use it when you want to guarantee that the access token hasn't been revoked.

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