Understanding Access Tokens vs. Refresh Tokens in Kubernetes Kubeconfig

🔹 Have you ever faced authentication failures in Kubernetes?
🔹 Wondered why your kubectl commands suddenly stop working?
🔹 Confused about how tokens in kubeconfig actually work?

If so, you’re not alone! Kubernetes authentication can be tricky, especially when dealing with tokens. One of the most common sources of confusion is the difference between an Access Token and a Refresh Token in a kubeconfig file.

This article will break down their roles, differences, and how they function in real-world Kubernetes authentication.

🔹 What is an Access Token in Kubernetes?

An Access Token is a credential that is passed with every request to the Kubernetes API server to prove the identity of the user. It is typically a JWT (JSON Web Token) issued by an Identity Provider (IdP) such as:

✅ Azure Active Directory (AAD) — for AKS
✅ Google Cloud IAM — for GKE
✅ AWS IAM/OIDC — for EKS
✅ OpenID Connect (OIDC) providers like Keycloak

Key Characteristics of an Access Token:

🔹 Short-lived — Typically expires in minutes or hours.
🔹 Used for API authentication — Sent in the request header for every kubectl command.
🔹 Stored in the kubeconfig file under users[].user.token.
🔹 Requires renewal once expired.

Example: Access Token in Kubeconfig

apiVersion: v1
kind: Config
users:
  - name: my-cluster-user
    user:
      token: eyJhbGciOiJIUzI1...

Here, the token is an Access Token that kubectl sends with every API request.

How Access Tokens Work in Kubernetes Authentication

1️⃣ You log in using an authentication method (kubectl login, az aks get-credentials, etc.).
2️⃣ A short-lived Access Token is issued and stored in kubeconfig.
3️⃣ Every time you run a command (kubectl get pods), this token is sent to the Kubernetes API server.
4️⃣ Once the token expires, the request fails with a 401 Unauthorized error.

At this point, Kubernetes does not automatically renew the token — this is where a Refresh Token comes in.

🔹 What is a Refresh Token in Kubernetes?

A Refresh Token is a long-lived credential that is not used for direct authentication but can be exchanged for a new Access Token when the current one expires.

Key Characteristics of a Refresh Token:

🔹 Long-lived — Can last days, weeks, or longer.
🔹 Not sent with API requests — Only used for obtaining a new Access Token.
🔹 Not stored in kubeconfig – Instead, managed by external authentication mechanisms.
🔹 Used in OIDC-based authentication – Works with authentication plugins to renew tokens seamlessly.

How Refresh Tokens Work in Kubernetes Authentication

1️⃣ When an Access Token expires, Kubernetes denies API requests.
2️⃣ If you are using an OIDC provider or authentication plugin, kubectl automatically requests a new Access Token using the Refresh Token.
3️⃣ The new Access Token replaces the expired one in kubeconfig, allowing commands to continue working.
4️⃣ If the Refresh Token itself expires, you must reauthenticate manually (e.g., using az aks get-credentials or kubectl oidc login).

Key Differences: Access Token vs. Refresh Token

FeatureAccess TokenRefresh TokenPurposeAuthenticates API requestsUsed to get a new Access TokenLifetimeShort-lived (minutes/hours)Long-lived (days/weeks)UsageSent with each kubectl API requestUsed when the Access Token expiresStorage in kubeconfigStored under users[].user.tokenTypically not stored, managed externallyRenewalCannot renew itself, expires quicklyUsed to get a fresh Access TokenSecurity RiskIf exposed, can be used for API accessIf exposed, can be used to generate new tokens

Real-World Example: Kubernetes Authentication with Azure Kubernetes Service (AKS)

If you use Azure Kubernetes Service (AKS), you’ve likely run this command:

az aks get-credentials --resource-group my-rg --name my-cluster

Here’s what happens behind the scenes:

✅ Step 1: Azure AD issues an Access Token and stores it in kubeconfig.
✅ Step 2: You run kubectl get pods, and the Access Token is sent to the API server.
✅ Step 3: If the token expires, Azure CLI can automatically renew it using a Refresh Token.
✅ Step 4: If the Refresh Token also expires, you must re-run az aks get-credentials to reauthenticate.

This automatic renewal is handled by Azure’s authentication plugin, making the process seamless for developers.

Why Does This Matter?

✅ Prevents authentication failures — Knowing how tokens work helps avoid downtime.
✅ Improves security — Refresh Tokens reduce the risk of long-lived access credentials being compromised.
✅ Enhances troubleshooting — If kubectl stops working, checking the token expiration can quickly diagnose the issue.
✅ Cloud-agnostic knowledge – The same concepts apply to AKS, GKE, EKS, and other Kubernetes clusters using OIDC authentication.

Best Practices for Managing Tokens in Kubernetes

🔹 Use short-lived Access Tokens — Avoid long-lived API tokens that pose security risks.
🔹 Enable automatic token renewal — Use an OIDC authentication plugin to refresh tokens seamlessly.
🔹 Monitor expiration times — If kubectl fails unexpectedly, check token validity.
🔹 Avoid storing sensitive tokens in scripts or hardcoded files – Use secrets management solutions.

Final Thoughts

Understanding Access Tokens vs. Refresh Tokens is crucial for anyone managing Kubernetes clusters. By leveraging OIDC authentication and token refresh mechanisms, you can ensure a seamless and secure experience when working with kubectl and cloud-based Kubernetes services.