X402.Facilitator.Auth.CDP (X402 v0.5.0)

Authentication for the Coinbase Developer Platform (CDP) x402 facilitator.

CDP's hosted facilitator (facilitator_url/0) requires an Authorization: Bearer <JWT> header on every request. The JWT is an EdDSA or ES256 signed token carrying the API key id and a uris claim binding it to the exact request.

API keys

Credentials are passed to new/1 via the :api_key_id and :api_key_secret options. In applications that want a single source of truth at runtime, put them in application configuration and let the facilitator resolve them (see the otp_app option on X402.Facilitator.start_link/1):

# config/runtime.exs
config :my_app, MyX402,
  auth: {X402.Facilitator.Auth.CDP,
         api_key_id: System.fetch_env!("CDP_API_KEY_ID"),
         api_key_secret: System.fetch_env!("CDP_API_KEY_SECRET")}

Two API key secret formats are supported, matching the CDP SDK:

Ed25519 — base64 of the 64-byte private key (32-byte seed + 32-byte public key). This is the default for new API keys.
EC (P-256) — a PEM EC PRIVATE KEY (SEC1) or PKCS#8 private key. Used by legacy API keys.

The secret format is detected automatically; no configuration is required.

Usage

X402.Facilitator.start_link(
  finch: MyFinch,
  url: X402.Facilitator.Auth.CDP.facilitator_url(),
  auth: {X402.Facilitator.Auth.CDP, api_key_id: "...", api_key_secret: "..."}
)

The JWT is generated per facilitator operation with a fresh nonce and timestamps. Transport retries reuse it within its 120-second validity window. The aud claim is intentionally omitted to match the reference CDP SDK's x402 facilitator client.

Summary

Types

key_format()

API key secret format.

t()

CDP auth state.

Functions

facilitator_url()

Returns the CDP x402 facilitator base URL.

headers(auth, map)

Builds the Authorization (and Correlation-Context) headers for a request.

new(opts)

Builds CDP auth state from :api_key_id and :api_key_secret options.

Types

key_format()

@type key_format() :: :ed25519 | :ecdsa_p256

API key secret format.

t()

@type t() :: %X402.Facilitator.Auth.CDP{
  api_key_id: String.t(),
  key_format: key_format(),
  key_material: binary()
}

CDP auth state.

Functions

facilitator_url()

(since 0.5.0)

@spec facilitator_url() :: String.t()

Returns the CDP x402 facilitator base URL.

Note that this URL is never used as a default; a facilitator must be configured with an explicit url: option.

headers(auth, map)

(since 0.5.0)

@spec headers(t(), X402.Facilitator.Auth.request_info()) ::
  {:ok, [{String.t(), String.t()}]}

Builds the Authorization (and Correlation-Context) headers for a request.

The JWT binds the request method, host, and path in its uris claim and is signed fresh for every call.

new(opts)

(since 0.5.0)

@spec new(keyword()) :: {:ok, t()} | {:error, term()}

Builds CDP auth state from :api_key_id and :api_key_secret options.

Returns {:error, reason} when credentials are missing or the secret is not a valid Ed25519 or P-256 key. For config-driven credentials, see the otp_app option on X402.Facilitator.start_link/1.