This library generates and verifies Proof Key for Code Exchange (PKCE) challenge pairs, which are used to enhance OAuth 2.0 security by preventing authorization code interception attacks. It provides functions to create code verifier and challenge pairs using either SHA-256 hashing (S256) or plain text (plain), and includes verification capabilities to ensure the integrity of the generated pairs. The library is designed for developers implementing OAuth 2.0 authentication flows in JavaScript applications, particularly those building mobile apps, single-page applications, or public clients that need to securely handle authorization codes without exposing client secrets.