import { AuthCredentials, AuthResponse } from "./types";
/**
 * Authenticates the merchant and returns a session token.
 * @param baseUrl The base URL for the Nass Payment Gateway API.
 * @param credentials Merchant username and password.
 * @returns An object containing the access token.
 * @throws {Error} If authentication fails (e.g., 401 Unauthorized, 400 Bad Request).
 */
export declare function authenticate(baseUrl: string, credentials: AuthCredentials): Promise<AuthResponse>;