Overview

If you are building a modern app or API, you likely 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, which your application can then use. It is important that your application only uses the access token to grant access, and not the ID token. For more information about this, see the Access Tokens vs ID Tokens section below.

Once the signed tokens are issued to the end users they can be passed to your application, which must validate them. There are two ways to verify a token: locally, or remotely with Okta. The token has been signed with a JSON Web Key (JWK) using the RS256 algorithm. To validate the signature, Okta provides your application with a public key that can be used.

We will now cover the terms used in this document, and an explanation of why you should use access tokens instead of ID tokens for this use case.

• If you'd like to jump straight to the local validation steps: What to Check When Validating an Access Token
• If you'd like to see how to validate a token directly with Okta: Validating A Token Remotely With Okta
• If you want to see specifically how to accomplish this in your language of choice: Okta Libraries to Help You Verify Access Tokens

A high-level overview of OAuth 2.0 can be found here.

The access tokens are in JSON Web Token (JWT) format. They are signed using asynmmetrical JSON Web Keys (JWK).

More information about Okta's access tokens can be found in the OIDC & OAuth 2.0 Reference.

Access Tokens vs ID Tokens

As mentioned above, it is important that the resource server (your server-side application) accept only the access token from a client. This is because access tokens are intended for authorizing access to a resource.

ID Tokens, on the other hand, are intended for authentication. They provide information about the resource owner, to allow you verify that they are who they say they are. Authentication is the concern of the clients. Because of this, when a client makes an authentication request, the ID Token that is 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 and parse your Okta JSON Web Keys (JWK), which should be checked periodically and cached by your application.
• Decode the access token, which is in JSON Web Token format
• Verify the signature used to sign the access token
• Verify the claims found inside the access token

Retrieve The JSON Web Keys

The JSON Web Keys (JWK) need to be retrieved from your Okta Authorization Server, though your application should have them cached. Specifically, your Authorization Server's Metadata endpoint contains the jwks_uri, which you can use to get the JWK.

For more information about retrieving this metadata, see Retrieve Authorization Server Metadata.

Decoding and Validating the Access Token

You will have to decode the access token, which is in JWT format. This involves the following steps:

• Verify the Token Signature
• Verify the Claims

Okta provides libraries to perform these steps for you:

• Go
• Java
• Node.js
• PHP

This code uses the Okta JWT Verifier for Golang.

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

• Signature is valid (the token was signed by a private key which has a corresponding public key in the JWKS response from the authorization server).
• Access token is not expired (requires local system time to be in sync with Okta, 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 the verifier is constructed with.
• Any 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"] = "{CLIENT_ID}"

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

verifier := jwtVerifierSetup.New()

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

You may need to adjust your clock skew leeway. We default 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

Don't see the language you're working in? Get in touch: developers@okta.com

Validating A Token Remotely With Okta

Alternatively, you can also validate an access or refresh Token using the Token Introspection endpoint: Introspection Request. This endpoint takes your token as a URL query parameter and returns back a simple JSON response with a boolean active property.

This incurs a network request which is slower to do verification, but can be used when you want to guarantee that the access token hasn't been revoked.

Support

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