import { Request, Middleware } from "./";
export declare type WithHeaderValue<Req> = string | string[] | {
    (request: Req): string | string[];
};
/**
 * Add a header to the request that can either override, or be overridden
 * by, the headers in the request.
 */
export declare function withHeader<CustomRequestOptions extends object = any>(name: string, value: WithHeaderValue<Request<any, CustomRequestOptions>>, override?: boolean): Middleware<Request<any, CustomRequestOptions>, any>;