import { Options as bodyParserOptions } from 'koa-bodyparser';
import Koa from 'koa';
declare type SecretKeyReturnFunction = (key: string) => string | undefined;
declare type SecretKeyPromiseFunction = (key: string) => Promise<string>;
declare type SecretKeyCallbackFunction = (key: string, callback: ((error: Error) => void) | ((error: undefined, secret: string) => void)) => void;
declare type SecretForKeyFunction = SecretKeyReturnFunction | SecretKeyPromiseFunction | SecretKeyCallbackFunction;
declare type onAcceptedFunction = (ctx: Koa.Context, next: Koa.Next) => void;
declare type onRejectedFunction = (ctx: Koa.Context, next: Koa.Next, error: Error) => void;
interface SimpleHMACAuthKoaOptions {
    secretForKey: SecretForKeyFunction;
    onAccepted?: onAcceptedFunction;
    onRejected: onRejectedFunction;
    bodySizeLimit: number;
    bodySizeLimitString?: string;
    bodyParser: bodyParserOptions;
}
/**
 * Return Koa middleware that authenticates incoming requests
 *
 * @param {object} options
 * @param {function} options.secretForKey - function that returns the secret for a specified API key. Can be a promise, direct return, or invoke the 2nd callback parameter
 * @param {function} [options.onRejected] - function invoked when a request fails authentication
 * @param {function} [options.onAccepted] - optional function invoked when a request passes authentication
 * @param {object} [options.bodyParser] - body parser parameters
 * @param {Array} [options.bodyParser.enableTypes=['json', 'form', 'text']] - optionally parse only a subset of data types
 * @returns {function} middleware function
 */
declare function middleware(options?: Partial<SimpleHMACAuthKoaOptions>): Koa.Middleware;
export default middleware;