/**
 * Generate a cryptographically random code verifier for PKCE
 * Per RFC 7636, the code verifier must be:
 * - 43-128 characters long
 * - Use only unreserved URI characters: [A-Za-z0-9-._~]
 */
export declare function generateCodeVerifier(): string;
/**
 * Calculate the code challenge from a code verifier using S256 method
 * Per RFC 7636: code_challenge = BASE64URL(SHA256(code_verifier))
 * @param verifier The code verifier string
 * @returns The code challenge (base64url-encoded SHA256 hash)
 */
export declare function calculateCodeChallenge(verifier: string): string;
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