HTTP Basic Auth Header Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching http basic auth header, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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

# HTTP Basic Auth Header
# ReDoS-safe | RegexVault — Web & Network > HTTP

import re

http_basic_auth_header_pattern = re.compile(r'^Basic ([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$')

def validate_http_basic_auth_header(value: str) -> bool:
    return bool(http_basic_auth_header_pattern.fullmatch(value))

# Example
print(validate_http_basic_auth_header("Basic dXNlcjpwYXNz"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > HTTP 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

Capture group 2 or 3 contains the base64 credentials. Decode to extract username:password — the colon is the delimiter. Never log decoded Basic Auth credentials.