API Key

A secret credential used to authenticate with an API service — the traditional model that x402 aims to replace for agent-to-service interactions.

An API key is a unique identifier used to authenticate requests to an API. Traditionally, developers sign up for a service, generate an API key, and include it in request headers. This model has problems for AI agents: keys must be pre-provisioned by humans, each service requires its own key, and keys grant unlimited access within rate limits (no per-call billing). The x402 protocol replaces API keys with payment-as-authentication: any agent with funds can call any x402 service without pre-registration. Mithril still uses an API key for its own management API, but the services in the catalog are accessed via x402.