KB:How OIDC Connects AKS Service Accounts to Azure Managed Identities MI

OIDC (OpenID Connect) is the glue that binds the Kubernetes Service Account (SA) → Azure Managed Identity (MI) → Federated Credential chain.

Here’s what’s really happening behind the scenes in AKS + Microsoft Entra ID (formerly Azure AD).

🔐 The Role of OIDC in the AKS–Azure Identity Chain

1. OIDC Issuer: The Cluster’s Identity Provider

When you enable OIDC on your AKS cluster, Azure assigns it an OIDC issuer URL, like:

https://eastus.oic.prod-aks.azure.com/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/

This URL acts like a mini identity provider (IdP) for your cluster.

Inside the cluster, Kubernetes Service Accounts can issue JWT tokens that are signed by this OIDC issuer.
Each token includes claims like:

  • iss → the OIDC issuer URL

  • sub → system:serviceaccount:<namespace>:<serviceaccount>

  • aud → the audience you request when you create the token

Those claims prove “This token was issued by this AKS cluster for this Service Account.”

2. Federated Credential: The Bridge to Entra ID

In Microsoft Entra (Azure AD), you create a Federated Credential inside a User-Assigned Managed Identity (UAMI) or an App Registration.

That federated credential tells Entra ID:

“I trust tokens coming from this OIDC Issuer URL, but only if the sub claim matches system:serviceaccount:<namespace>:<serviceaccount>.”

So when your Kubernetes pod (running with that SA) requests an Azure token:

  1. The pod gets a signed OIDC JWT from the AKS OIDC endpoint.

  2. The pod presents that token to Azure’s identity endpoint.

  3. Entra ID validates:

    • The signature (via the OIDC Issuer’s JWKS keys),

    • The iss (issuer matches the URL you entered),

    • The sub (matches the SA you configured in the federated credential).

If all checks out — ✅ Azure issues an access token for the Managed Identity.

3. Managed Identity: The Azure-side Actor

Once the token is issued, your workload in the pod is acting as that Managed Identity — it can:

  • Authenticate to Azure Resource Manager,

  • Access Key Vault, Storage, Cosmos DB, etc.

  • All without storing secrets or client secrets in the pod.

So in plain English:

OIDC = the authentication handshake
Federated Credential = the trust mapping
Managed Identity = the Azure persona
Service Account = the Kubernetes persona

And the handshake path is:

K8s Service Account  →  AKS OIDC Issuer  →  Entra Federated Credential  →  Managed Identity  →  Azure Resource Access

🧩 Visual summary

[ Pod ]
   |
   └── uses ServiceAccount (namespace: dev, name: my-app-sa)
         |
         └── AKS issues OIDC JWT token (iss + sub)
                |
                └── Azure Entra ID Federated Credential validates it
                       |
                       └── issues Azure access token for Managed Identity

⚙️ Why this matters

  • No secrets — eliminates need for AZURE_CLIENT_SECRET.

  • Per-pod identity — each pod can have its own Managed Identity securely.

  • Automatic rotation — JWTs and access tokens are short-lived.

  • Cross-cloud portability — same concept works in GKE, EKS, etc. (each has its own OIDC issuer).

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