import type { PkceChallenge } from '../../types/index.js';
/**
 * Generate a random code verifier (URL-safe base64, no padding).
 * The verifier is kept secret by the client and sent at the token exchange step.
 */
export declare function generateCodeVerifier(): string;
/**
 * Derive the S256 code challenge from a verifier.
 * challenge = BASE64URL(SHA-256(ASCII(verifier)))
 */
export declare function deriveCodeChallenge(verifier: string): string;
/**
 * Generate a complete PKCE challenge pair (verifier + S256 challenge).
 * Both values are URL-safe base64 without padding.
 */
export declare function generatePkceChallenge(): PkceChallenge;
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