/**
 * Generates a cryptographically random PKCE `code_verifier` per RFC 7636
 * §4.1. 43 base64url characters, 256 bits of entropy.
 */
export declare function generateCodeVerifier(): string;
/**
 * Derives the PKCE S256 `code_challenge` for the given verifier per
 * RFC 7636 §4.2: `BASE64URL(SHA256(ASCII(verifier)))`.
 *
 * @param verifier The PKCE verifier produced by `generateCodeVerifier`.
 */
export declare function deriveCodeChallenge(verifier: string): string;
/**
 * Generates a cryptographically random OAuth `state` value for CSRF
 * protection. 22 base64url characters, 128 bits of entropy.
 */
export declare function generateState(): string;