Files
xamxam/nginx/PHP_AUTH_LAYER.md
Théophile Gervreau-Mercier 8613f71112 security: add PHP session auth guard for admin panel (item #2, CRITICAL)
- lib/AdminAuth.php: new class with requireLogin(), login(), logout(),
  isAuthenticated(); starts session with hardened cookie params
  (HttpOnly, SameSite=Strict, Secure, Path=/admin) — also resolves
  item #8 (session cookie hardening)
- requireLogin() auto-authenticates from nginx Basic Auth credentials
  ($_SERVER['PHP_AUTH_PW']) so the user only sees one browser prompt;
  falls back to /admin/login.php if the proxy is absent/misconfigured
- config/admin_credentials.php: gitignored credential store; define
  ADMIN_PASSWORD_HASH with a bcrypt hash to enable PHP auth
- config/admin_credentials.example.php: template for the above
- config/bootstrap.php: auto-loads admin_credentials.php if present
- .gitignore: exclude config/admin_credentials.php
- public/admin/login.php: fallback login form (shown only when nginx
  Basic Auth is bypassed / proxy absent)
- public/admin/logout.php: session destruction + redirect to login
- All 7 admin PHP files: replace session_start() with
  AdminAuth::requireLogin() (defence-in-depth behind nginx Basic Auth)
- public/admin/inc/head.php: Déconnexion button when ADMIN_PASSWORD_HASH
  is defined
- nginx/PHP_AUTH_LAYER.md: documents dual-auth architecture, UX flow,
  and setup instructions
- docs/TODO.SECURITY.md: items #2 and #8 moved to Resolved; priority
  order updated (all CRITICAL done)
2026-02-08 14:22:45 +01:00

115 lines
3.8 KiB
Markdown

# PHP Session Auth Layer — Admin Panel
> Addresses: **TODO item #2** (No PHP-level authentication in admin panel — 🔴 CRITICAL)
---
## Overview
The admin panel uses **two independent authentication layers** with a single UX prompt:
| Layer | Mechanism | Configured by |
|-------|-----------|---------------|
| **1st** | nginx HTTP Basic Auth | `/etc/nginx/.htpasswd-posterg` (see `ADMIN_USERS.md`) |
| **2nd** | PHP session guard (`lib/AdminAuth.php`) | `config/admin_credentials.php` |
The user only sees **one prompt** (the browser Basic Auth dialog). PHP reads the
same password from `$_SERVER['PHP_AUTH_PW']` and validates it independently with
`password_verify`. On success it creates a session so subsequent requests skip
the `password_verify` call.
---
## Why two layers?
nginx Basic Auth alone is a **single point of failure**:
- Reverse-proxy misconfiguration could expose admin routes directly.
- Local development without the proxy leaves admin unprotected.
- A misconfigured `auth_basic off` block (e.g., in a nested location) could bypass it.
The PHP session guard (`AdminAuth::requireLogin()`) is ~100 lines of PHP stdlib
(`password_verify` + `session_regenerate_id`) with negligible attack surface.
## Authentication flow
```
Browser → nginx Basic Auth dialog (username + password)
nginx validates against .htpasswd ──✗──▶ 401
│ ✓
PHP: AdminAuth::requireLogin()
├─ session already live? ──✓──▶ proceed
├─ $_SERVER['PHP_AUTH_PW'] set?
│ └─ password_verify(PHP_AUTH_PW, ADMIN_PASSWORD_HASH)
│ ├─ ✓ → create session → proceed (normal path)
│ └─ ✗ → redirect to login form
└─ neither → redirect to login form (proxy bypass)
```
The login form (`/admin/login.php`) is a **fallback** for when the reverse proxy
is absent. In normal production use the user never sees it.
---
## PHP auth setup (production)
1. Generate a bcrypt hash for the admin password:
```bash
php -r "echo password_hash('your-secret-password', PASSWORD_DEFAULT);"
```
2. Create `config/admin_credentials.php` (outside the webroot, never committed):
```php
<?php
define('ADMIN_PASSWORD_HASH', '$2y$12$<paste-hash-here>');
```
3. The `bootstrap.php` auto-loads this file if it exists.
If `ADMIN_PASSWORD_HASH` is not defined (development / cli-server), the PHP
auth layer is a **no-op** — nginx Basic Auth remains the sole guard.
---
## Session cookie hardening (TODO item #8)
`AdminAuth::startSession()` calls `session_set_cookie_params()` before
`session_start()`, applying:
| Attribute | Value |
|-----------|-------|
| `HttpOnly` | `true` |
| `SameSite` | `Strict` |
| `Secure` | `true` (disabled on cli-server for dev) |
| `Path` | `/admin` |
| `Lifetime` | `0` (session cookie, expires on browser close) |
This replaces all direct `session_start()` calls in admin PHP files.
---
## Logout
A **Déconnexion** button is shown in the admin nav when `ADMIN_PASSWORD_HASH`
is defined. It hits `/admin/logout.php` which destroys the PHP session.
nginx Basic Auth invalidation requires closing the browser tab / window.
---
## Files changed
| File | Change |
|------|--------|
| `lib/AdminAuth.php` | New — auth guard class |
| `config/admin_credentials.php` | New — credential store (gitignored) |
| `config/admin_credentials.example.php` | New — example / template |
| `config/bootstrap.php` | Load credentials on startup |
| `public/admin/*.php` | Replace `session_start()` with `AdminAuth::requireLogin()` |
| `public/admin/actions/*.php` | Same |
| `public/admin/login.php` | New — login form |
| `public/admin/logout.php` | New — logout handler |
| `public/admin/inc/head.php` | Logout button in nav |