import { Request, Response, NextFunction } from "express";
export declare const audienceRegex: RegExp;
interface Options {
    audience?: string;
    iapProjectNumber?: string;
    iapServiceID?: string;
}
export declare function required<T>(value: T | undefined | null, fieldName: string): T;
export declare function validateAudience(audience: string | undefined): void;
export declare const authenticationMiddleware: (opts: Options) => (req: Request, _: Response, next: NextFunction) => Promise<void>;
export {};