PKCE Code Verifier Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching pkce code verifier, ported and verified for Python. 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 Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# PKCE Code Verifier
# ReDoS-safe | RegexVault — Security > OAuth & OIDC

import re

pkce_code_verifier_pattern = re.compile(r'^[A-Za-z0-9\-._~]{43,128}$')

def validate_pkce_code_verifier(value: str) -> bool:
    return bool(pkce_code_verifier_pattern.fullmatch(value))

# Example
print(validate_pkce_code_verifier("dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"))  # 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 Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. 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.