import { ExoConnection } from '../../ExoConnection/ExoConnection';
export declare const dangerouslyDisableDefaultSrc: unique symbol;
export interface HelmetOpts {
    contentSecurityPolicy?: HelmetContentSecurityPolicyOpts | boolean;
    crossOriginEmbedderPolicy?: HelmetCrossOriginEmbedderPolicyOpts | boolean;
    crossOriginOpenerPolicy?: HelmetCrossOriginOpenerPolicyOpts | boolean;
    crossOriginResourcePolicy?: HelmetCrossOriginResourcePolicyOpts | boolean;
    originAgentCluster?: boolean;
    referrerPolicy?: HelmetReferrerPolicyOpts | HelmetReferrerPolicyOpts[] | boolean;
    strictTransportSecurity?: HelmetStrictTransportSecurityOpts | boolean;
    noSniff?: boolean;
    dnsPrefetchControl?: boolean | null;
    permittedCrossDomainPolicies?: HelmetPermittedCrossDomainPoliciesOpts | boolean;
    xssProtection?: boolean;
}
export type HelmetCrossOriginEmbedderPolicyOpts = 'require-corp' | 'credentialless' | 'unsafe-none';
export type HelmetCrossOriginResourcePolicyOpts = 'same-origin' | 'same-site' | 'cross-origin';
export type HelmetCrossOriginOpenerPolicyOpts = 'same-origin' | 'same-origin-allow-popups' | 'unsafe-none';
export type HelmetPermittedCrossDomainPoliciesOpts = 'none' | 'master-only' | 'by-content-type' | 'all';
export type HelmetReferrerPolicyOpts = 'no-referrer' | 'no-referrer-when-downgrade' | 'same-origin' | 'origin' | 'strict-origin' | 'origin-when-cross-origin' | 'strict-origin-when-cross-origin' | 'unsafe-url' | '';
export type HelmetContentSecurityPolicyDirFunc = (conn: ExoConnection) => string;
export type HelmetContentSecurityPolicyDirValue = string | HelmetContentSecurityPolicyDirFunc;
export type HelmetContentSecurityPolicyDir = Record<string, null | Iterable<HelmetContentSecurityPolicyDirValue> | typeof dangerouslyDisableDefaultSrc>;
export interface HelmetContentSecurityPolicyOpts {
    useDefaults?: boolean;
    directives?: HelmetContentSecurityPolicyDir;
    reportOnly?: boolean;
}
export interface HelmetStrictTransportSecurityOpts {
    maxAge?: number;
    includeSubDomains?: boolean;
    preload?: boolean;
}