Harden Your API Access Using Workload Identity Management

Read full article from Curity here:  https://curity.io/resources/learn/workload-identities/?utm_source=nhimg

Workload identities are non-human identities, identities assigned to software components rather than people. They can represent API clients, microservices, or any automated workloads in your system architecture, both on the user-facing side and in the backend.

By providing a reliable way to authenticate workloads, workload identities are a powerful tool for securing API access. This article explains what they are, how they work, and how to combine them with OAuth for a robust API security strategy.

What Is a Workload Identity?

A workload identity is a managed identity issued to a software component by a trusted platform (e.g., cloud provider or Kubernetes). It allows the workload to prove its identity to other services securely.

A workload identity typically consists of:

1. Workload Identifier: A unique ID distinguishing the workload from others.
2. Workload Credential: A short-lived token issued by the platform.
3. Optional Private Key: Used with the credential for cryptographic proof of identity.

The platform attests the workload identifier and issues a credential, often automatically renewed to avoid the overhead of manual credential management.

What Is a Workload Credential?

A workload credential is a verifiable, short-lived document (often JWT or X.509 certificate) that proves the identity of a workload. When combined with a private key, the workload can authenticate securely to other services without exposing long-term secrets.

Key benefits include:

• Automatic renewal without workload intervention
• Strong asymmetric cryptography
• Reduced risk of credential leakage

Standardization and Initiatives

Several initiatives aim to standardize workload identities:

• WIMSE: Best practices for workload identities in data security solutions.
• SPIFFE/SPIRE: Provides interoperability for workloads across cloud and on-premise environments.

Key Use Cases for APIs

Workload identities excel at authentication for API clients and microservices. Common use cases include:

1. Strengthening Client Credentials

• Replace static API keys or passwords with workload credentials.
• Credentials are automatically renewed, reducing exposure from leaks.
• Useful for internal microservice-to-microservice communication.

2. Confidential Connections

• Platforms like Istio or service meshes use workload identities to enforce mutual TLS (mTLS) for internal connections.
• Encrypts data in transit and automatically renews TLS certificates via sidecars or platform services.

3. Workload Authorization

• Once workloads are authenticated, authorization policies can restrict what each workload can access.
• Examples:
  • AWS IAM roles for service accounts
  • Kubernetes RBAC for pod-level access

Note: Workload identities do not replace API authorization. APIs still need to enforce proper access control and business rules.

Integrating Workload Identities with OAuth

OAuth provides access tokens for API clients. Best practices recommend using confidential clients with strong credentials for token requests.

Workload credentials can serve as strong client credentials in OAuth flows:

1. Backend Clients

• Use X.509 certificates or JWT assertions to authenticate workloads with the authorization server.
• Example: Client Credentials Flow using JWT assertion:

POST /token HTTP/1.1

HOST: login.example.com

Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials

client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer

client_assertion=eyJhbGciOiJQUzI1NiJ9.eyJpc3MiOiJ3b3JrbG9hZC...

• Platforms like Kubernetes can issue service account tokens that act as JWT assertions for OAuth authentication.

2. External Clients

• Mobile or IoT apps can use attestation JWTs or X.509 certificates as proof of identity.
• The authorization server validates the attestation before issuing access tokens.

Workload identities in OAuth strengthen client authentication without introducing long-term secrets, enabling scalable and secure API access.

Limitations

• Workload identities are primarily authentication mechanisms, not full authorization solutions.
• APIs must still enforce business logic and access control after verifying a workload’s identity.
• Confidentiality depends on proper token management and platform trust.

Summary

Workload identities provide strong, manageable credentials for software workloads, enabling:

• Strong client authentication using asymmetric cryptography
• Automatic credential renewal for scalability
• Encrypted internal connections (mTLS)
• Integration with OAuth for secure access token issuance

To implement robust API security, combine workload identities with OAuth-based authorization, ensuring both authentication and proper access control.