PKCE Code Verifier Regex for PHP

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching pkce code verifier, ported and verified for PHP. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// PKCE Code Verifier
// ReDoS-safe | RegexVault — Security > OAuth & OIDC

define('PKCE_CODE_VERIFIER_PATTERN', '/^[A-Za-z0-9\-._~]{43,128}$/');

function validate_pkce_code_verifier(string $input): bool {
    return (bool) preg_match(PKCE_CODE_VERIFIER_PATTERN, $input);
}

// Example
var_dump(validate_pkce_code_verifier("dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Security > OAuth & OIDC category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

RFC 7636 PKCE: code_verifier is a random string 43-128 chars from [A-Za-z0-9-._~]. code_challenge = BASE64URL(SHA256(code_verifier)) for S256 method. PKCE is mandatory for public clients (SPAs, mobile apps) and recommended for all clients.