php-session-auth

A security guide for login, registration, logout, and session handling in framework-free PHP applications. It covers password storage, CSRF protection, secure sessions, lockouts, and preventing user-account leaks.

In plain words
What is it for?
Use it when building or reviewing vanilla PHP authentication with password hashing, normalized emails, CSRF-protected forms, session renewal, and brute-force defenses.
Why use it?
It addresses common weaknesses in hand-built authentication, such as weak password handling, session fixation, missing request protection, and unlimited login attempts.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/maludb-ed/htmx-php-builder/php-session-auth
Any agent
npx skills add maludb-ed/htmx-php-builder --skill php-session-auth
Clone the repo
git clone --depth 1 https://github.com/maludb-ed/htmx-php-builder

Made for: Claude Code, Codex.

Per session 56 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,923 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00056 $0.01923
Opus 5 $0.00028 $0.00962
Sonnet 5 $0.00011 $0.00385
Haiku 4.5 $0.00006 $0.00192

Measured 2d ago against content hash f73cb1579da8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

php-session-auth scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

$u = $stmt->fetch(PDO::FETCH_ASSOC);
skills/php-session-auth/SKILL.md · 135 lines

How it starts

The opening of the file, as written. The whole thing — 135 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Vanilla PHP Session Auth + CSRF

Overview

Building session auth in vanilla PHP is mostly solved by password_hash, hash_equals, and session_regenerate_id — agents apply those reliably. The failures are judgment calls this skill exists to fix: missing brute-force protection, un-normalized emails, CSRF guards that only cover POST, and "hardening" that is actually an anti-pattern.

Core principle: the cryptography is the easy part. The security comes from the policy around it — rate limits, normalization, what you choose not to do.

When to Use

  • Implementing login / registration / logout in PHP without a framework
  • Adding CSRF protection to state-changing forms
  • Reviewing hand-rolled PHP auth for security gaps

When NOT to use: Laravel/Symfony (their auth + CSRF are built in — use those, don't hand-roll).

Non-Negotiables (checklist)

Requirement Rule
Password storage password_hash($pw, PASSWORD_DEFAULT) + password_verify. Re-hash on login via password_needs_rehash.
Password length Min 12 chars; max 72 bytes (bcrypt silently truncates past 72).
Email Normalize: strtolower(trim($email)) before BOTH insert and lookup. Enforce a UNIQUE index and catch SQLSTATE 23000.
Session login session_regenerate_id(true) on every privilege change (login, logout, role change).
CSRF token Per-session, bin2hex(random_bytes(32)), compared with hash_equals. Rotate on login.
CSRF guard Validate on every unsafe method (POST, PUT, PATCH, DELETE) — not POST alone.
Brute force Rate-limit + lock login attempts per account AND per IP. Non-optional.
Enumeration Generic errors on login AND register; equalize timing with a precomputed dummy hash.
Cookies HttpOnly, Secure (in prod), SameSite=Lax.
Headers On auth pages: Cache-Control: no-store, X-Frame-Options: DENY, Referrer-Policy: same-origin.

Correct Patterns

Session bootstrap (before session_start()):

session_set_cookie_params([
    'lifetime' => 0, 'path' => '/', 'secure' => $isHttps,
    'httponly' => true, 'samesite' => 'Lax',
]);
ini_set('session.use_strict_mode', '1');   // reject attacker-supplied SIDs
ini_set('session.use_only_cookies', '1');
session_name('SID');
session_start();

Read the full file on GitHub · 135 lines

Files

What ships with it

2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 135 lines · 56 tokens per session scan A f73cb1579da8

Subscribe to this mod's changes

php-session-auth is a skill published in the GitHub repository maludb-ed/htmx-php-builder (8 stars, last pushed 26d ago), licensed MIT. It adds 56 tokens to every session and 1,923 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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