/** base64url with no padding (RFC 4648 §5). */
export declare function base64url(buf: Buffer): string;
/** 43-128 chars of the unreserved set. 32 random bytes -> 43 base64url chars. */
export declare function generateCodeVerifier(): string;
/** code_challenge = base64url(SHA256(code_verifier)), S256. */
export declare function computeCodeChallenge(verifier: string): string;
export declare const LOOPBACK_HOST = "localhost";
export declare const LOOPBACK_PATH = "/callback";
export declare function buildLoopbackRedirectUri(port: number): string;