January 22nd, 2006: There’s an updated version of this guide for WordPress 2 now: Securing WordPress 2 Admin Access With SSL

As one can guess from the look of this site, I’m using WordPress as my blog engine. At this time WordPress does not support HTTPS access to the admin area when the rest of the blog is served via normal HTTP. This is a bit unfortunate. I do not like logging in to my server over unencrypted connections, especially not when using public WLANs. Getting around this WordPress limitation requires quite a few steps:

The Goal

All communication involving passwords or authentication cookies should be done over HTTPS connections. wp-login.php and the wp-admin directory should only be accessible over HTTPS.
Normal reading access, as well as comments, tracebacks, and pingbacks still should go over ordinary HTTP.

The Plan

• Add an HTTPS virtual host that forwards requests to the HTTP virtual host
• Modify WordPress to send secure authentication cookies, so cookies never get sent over insecure connections accidentally
• Require a valid certificate on HTTPS clients. That means to log in to WordPress you need both a valid certificate and a valid password. If someone manages to get your password, he still can not login because he does not have a valid certificate.

The Implementation

Note: This documentation assumes a Debian sarge installation with Apache 2. Some things, in particular Apache module related ones, will be different on other systems.
The server used throughout the instructions is example.org/192.0.34.166. The server’s DocumentRoot is /blog and WordPress resides in /blog/wp. The value of WordPress’ home option is ‘http://example.org’ and the value of its site_url option is ‘http://example.org/wp’.

• Prepare the SSL certificates:
  • Generate your own certificate authority (CA) if you don’t have one already (I’m using the makefile from OpenSSL Certificate Authority Setup for managing mine) and import it into your browser.
  • Generate a certificate for the SSL server and certify it with your private CA.
  • Generate a certificate for your browser and certify it with your private CA. Most browsers expect a PKCS#12 file, so generate one with

    $ openssl pkcs12 -export -clcerts \
        -in blogclient.cert \
        -inkey blogclient.key \
        -out blogclient.p12

    Then import blogclient.p12 into your browser.

• Make WordPress SSL-ready:
  Apply this patch to the WordPress code. It makes the following changes:
  • Use secure authentication cookies in wp_setcookie()
  • Make check_admin_referer() working with HTTPS URLs
  • Disable login over XML-RPC
• Enable the necessary Apache modules:
  • Install mod_proxy_html. It will be used to replace absolute ‘http://example.org’ HTTP URLs in the WordPress output with ‘https://example.org’ HTTPS URLs:

    $ aptitude install libapache2-mod-proxy-html

    The module gets enabled automatically after installation.

  • Enable mod_proxy and mod_ssl

    $ a2enmod proxy
    $ a2enmod ssl

    Debian provides sane default configurations for both modules. You might want to take a look at the configuration files (ssl.conf and proxy.conf) nevertheless.

  • If you are compressing WordPress output (that is if you enabled the ‘WordPress should compress articles (gzip) if browsers ask for them’ option) then also enable mod_headers:

    $ a2enmod headers

• Configure Apache to listen on the HTTPS port

  $ cat > /etc/apache2/conf.d/ssl.conf << EOF
  <IfModule mod_ssl.c>
  	Listen 443
  </IfModule>
  EOF

• Modify the blog virtual host to limit access to wp-login.php and wp-admin to the local host. Also completely deny access to files which should never be accessed directly. Here is an example: 10-example.org
• Now setup the HTTPS virtual server: 20-example.org-ssl
  If you are compressing WordPress output you have to enable the RequestHeader line.
• Enable the site and restart Apache

  $ a2ensite 20-blog-ssl
  $ /etc/init.d/apache2 restart

• Remove the old WP cookies from your browser
• Test the new setup!