/**
 * Generates a high-entropy, cryptographically strong random string for use as a PKCE code verifier.
 * It uses rejection sampling to eliminate modulo bias, ensuring a perfectly uniform distribution
 * across the character set recommended by RFC 7636.
 *
 * @returns {string} A 64-character URL-safe random string.
 */
export declare const generateCodeVerifier: () => string;
/**
 * Stores the PKCE code verifier in sessionStorage.
 * @param {string} verifier - The verifier to store.
 */
export declare const setStoredCodeVerifier: (verifier: string) => void;
/**
 * Retrieves the PKCE code verifier from sessionStorage.
 * @returns {string | null}
 */
export declare const getStoredCodeVerifier: () => string | null;
/**
 * Removes the PKCE code verifier from sessionStorage.
 */
export declare const clearStoredCodeVerifier: () => void;