* Fix: Improve allowedHostnames .env configuration and fail-fast in production
Addresses GitHub issue #4480: .env app.allowedHostnames does not work as intended
## Problem
- CodeIgniter 4 cannot override array properties from .env
- Setting app.allowedHostnames.0, app.allowedHostnames.1 did NOT populate the array
- Application always fell back to 'localhost' silently in production
- Host header injection protection was effectively disabled
## Solution
1. Support comma-separated .env values: app.allowedHostnames = 'domain1.com,domain2.com'
2. Fail explicitly in production if not configured (throws RuntimeException)
3. Allow localhost fallback in development/testing with ERROR-level logging
4. Update documentation with clear setup instructions
## Changes
- app/Config/App.php: Parse comma-separated .env values, fail in production
- .env.example: Update format documentation
- INSTALL.md: Add prominent security section
- tests/Config/AppTest.php: Comprehensive tests for new behavior
Fixes#4480
Related: GHSA-jchf-7hr6-h4f3
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Co-authored-by: Ollama <ollama@steganos.dev>
Security: Prevent Host Header Injection attacks by validating HTTP_HOST
against a whitelist of allowed hostnames before constructing the baseURL.
Changes:
- Add getValidHost() method to validate HTTP_HOST against allowedHostnames
- If allowedHostnames is empty, log warning and fall back to 'localhost'
- If host not in whitelist, log warning and use first allowed hostname
- Update .env.example with allowedHostnames documentation
- Add security configuration section to INSTALL.md
- Add unit tests for host validation
This addresses the security advisory where the application constructed
baseURL from the attacker-controllable HTTP_HOST header, allowing:
- Login form phishing via manipulated form actions
- Cache poisoning via poisoned asset URLs
Fixes GHSA-jchf-7hr6-h4f3
