import type { RequestInterceptor } from './types.js';
/**
 * Adds an header to a request through an interceptor.
 *
 * @param key - The header key
 * @param value - The header value
 * @returns The Request interceptor
 *
 * @internal
 */
export declare const addHeaderInterceptor: (key: string, value?: string | undefined) => RequestInterceptor;
/**
 * Adds asynchronously an header to a request through an interceptor.
 *
 * @param key - The header key
 * @param value - The header value as a Promise
 * @returns The Request interceptor
 *
 * @internal
 */
export declare const addAsyncHeaderInterceptor: (key: string, getter: () => Promise<string | undefined>) => RequestInterceptor;