/**
 * Creates an Express middleware for Basic HTTP Authentication.
 *
 * This middleware checks for an `Authorization` header and validates
 * the username and password using base64-decoded credentials.
 *
 * If the credentials match, `next()` is called to proceed to the next middleware.
 * If the credentials are invalid or missing, a 401 Unauthorized response is sent.
 *
 * @function auth
 * @param {Object} data - Configuration object.
 * @param {string} data.login - The expected username.
 * @param {string} data.password - The expected password.
 * @param {function(import('express').Request, import('express').Response): import('express').Response} [data.customError] - Optional function `(req, res) => {}` called on auth failure.
 * @param {Function} [callback] - Optional fallback function `(req, res, next) => {}` executed after customError.
 *
 * @returns {function(import('express').Request, import('express').Response, import('express').NextFunction): void} Express middleware function.
 *
 * @example
 * import express from 'express';
 * import auth from './auth.mjs';
 *
 * const app = express();
 *
 * app.use(auth({
 *   login: 'admin',
 *   password: '1234',
 *   customError: (req, res) => {
 *     res.send('Custom unauthorized message');
 *   }
 * }));
 *
 * app.get('/', (req, res) => {
 *   res.send('Hello, authenticated user!');
 * });
 */
export default function auth(data: {
    login: string;
    password: string;
    customError?: ((arg0: import("express").Request, arg1: import("express").Response) => import("express").Response) | undefined;
}, callback?: Function): (arg0: import("express").Request, arg1: import("express").Response, arg2: import("express").NextFunction) => void;
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