/**
 * Zoe Middleware — Auth
 *
 * Simple, composable auth validation middleware.
 */
import type { PipelineContext, Middleware } from "../middleware.js";
export interface AuthOptions {
    /** Validate the request context. Throw or return false to reject. */
    validate: (ctx: PipelineContext) => boolean | Promise<boolean>;
    /** Error message on rejection (default: "Unauthorized") */
    errorMessage?: string;
}
/**
 * Create an auth middleware.
 *
 * @example
 * ```ts
 * const mw = authMiddleware({
 *   validate: (ctx) => !!ctx.metadata.apiKey,
 *   errorMessage: "API key required",
 * });
 * ```
 */
export declare function authMiddleware(options: AuthOptions): Middleware;