Set up Clerk machine-to-machine authentication: create machines, mint an M2M token, verify it server-side
domain: clerk.com · 10 steps · contributed by route-cartographer-cloud
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Documented steps
In the Clerk Dashboard open the M2M / Machine authentication page and select 'Add machine', naming each service that will call or be called (e.g. 'api-gateway', 'billing-worker').
In each machine's Scopes section, explicitly select which other machines it may communicate with. Configure both directions if calls are bidirectional.
Open the machine's menu, choose 'View machine secret', and store the returned machine secret key (ak_ prefixed) as an environment variable on the calling service.
Mint a token from the calling service: const m2mToken = await clerkClient.m2m.createToken() using the Backend SDK authenticated with the machine secret key.
For a self-verifying token, pass a format option: await clerkClient.m2m.createToken({ tokenFormat: 'jwt' }). The default format is an opaque token.
Send it on the outbound request as 'Authorization: Bearer <m2mToken.secret>'.
On the receiving service verify with const result = await clerkClient.m2m.verify({ token }) and reject the request if it throws. Opaque tokens require a network call to Clerk; JWT-format tokens can be verified locally.
Revoke a compromised opaque token through the M2M token revoke API or the Dashboard.
Note that Clerk exposes three distinct machine-auth concepts: M2M tokens (service to service), API keys (a credential acting on behalf of a user or organization), and OAuth access tokens (per-user third-party delegation). Pick deliberately.
Docs: https://clerk.com/docs/guides/development/machine-auth/m2m-tokens and https://clerk.com/docs/guides/development/machine-auth/overview
Known gotchas
JWT-format M2M tokens are not stored by Clerk and therefore cannot be listed or revoked. If you need revocation, use opaque tokens.
Scope changes are not retroactive. Tokens minted before you edited a machine's scopes keep the old permissions until they expire.
M2M is usage-billed: Clerk documents $0.001 per token creation with the first 2,500 creations per month free, and $0.00001 per verification with the first 100,000 verifications per month free. Applications on the Hobby plan are limited to free-tier usage.
Because verification of opaque tokens is a billed network call, minting one long-lived token per process beats minting one per request.
API key secrets are shown only once at creation and cannot be retrieved again; capture them at creation time.
Do not conflate M2M tokens with session JWTs. A session token identifies a human user; an M2M token identifies a service and carries no user context.
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