Custom OIDC Token Audiences

Vercel's OIDC issuer (oidc.vercel.com) now supports custom audiences. Deployments can request OIDC tokens with a specific audience claim, enabling secure service-to-service authentication with third-party providers.

Link to headingWhy custom audiences?

Vercel OIDC tokens are issued with a fixed audience (https://vercel.com/{owner}). While most cloud providers don't require a specific audience value, using a unique audience per provider is a security best practice. If a provider is compromised, an attacker cannot replay the token against a different provider - the mismatched aud claim will cause verification to fail. This new service makes it easy to mint provider-specific tokens without managing additional infrastructure.

Link to headingHow it works

When a Vercel deployment runs, it receives an OIDC token signed by Vercel. The new exchange service accepts this token and returns a new one signed with the same key, but with an updated audience (aud) claim targeting your downstream service.

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import { awsCredentialsProvider } from '@vercel/oidc-aws-credentials-provider';
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import { S3Client } from '@aws-sdk/s3-client';
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const s3 = new S3Client({
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  region: 'us-east-1', 
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  credentials: awsCredentialsProvider({
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    // The token's `aud` claim will be set to sts.amazonaws.com
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    audience: 'sts.amazonaws.com',
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    clientConfig: { region: 'us-east-1' },
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  }),
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});

The exchanged token:

• Preserves all original claims (project, environment, owner, expiration)

• Sets the iss (issuer) to https://oidc.vercel.com/{owner}, scoped to the team that owns the deployment

• Includes an act (actor) claim with the original token's audience and issued-at time, providing an auditable delegation chain

• Updates the aud to the requested downstream audience

• Updates the iat (issued-at) to the current timestamp, reflecting when the new token was created

You can optionally pass a jti (JWT ID) to assign a unique identifier to the exchanged token. This is useful for auditing and tracing token usage across services - for example, correlating a specific token exchange with downstream API calls in your logs.

Downstream services verify the exchanged token using the public key available at https://oidc.vercel.com/{owner}/.well-known/jwks.

Both the signing key and the token exchange endpoint are replicated across all Vercel regions, ensuring low-latency token exchange regardless of where the deployment is running.