How to log POST request data in Apache

Apache Access Log records incoming HTTP requests to the server, and CustomLog directive defines what is kept in the log. The following is an example HTTP request, CustomLog directive, and the corresponding log that it captures:

GET /apache/log-post?field01=value01&field02=value02 HTTP/1.1
Host: simplified.guide
Content-Type: application/x-www-form-urlencoded

LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined

52.46.36.182 - - [30/Jan/2020:18:04:53 +0000] "GET /apache/log-post?field01=value01&field02=value02 HTTP/1.1" 200 13375 "-" "Amazon CloudFront"

The above CustomLog directive is sufficient if you're only logging GET requests, as, by default, Apache can log the HTTP request headers. However, by default, it is not able to log POST requests as POST requests involve sending data in the body of the request.

You can log POST request details by using dumpio module for Apache, which allows logging of HTTP request body.

1. Enable dumpio module for Apache.

   $ sudo a2enmod dump_io # Ubuntu and Debian
   Enabling module dump_io.
   To activate the new configuration, you need to run:
     systemctl restart apache2
   $ sudo a2enmod dumpio # SUSE

   • Distribution with a2enmod support can simply run the command above without having to manually enable the required modules.
   • Fedora, CentOS and Red Hat enables the module by default so requires no manual action to enable the modules.

   Related: How to enable or disable Apache modules

   Options	Debian, Ubuntu	openSUSE and SLES	Fedora Core, CentOS, RHEL	macOS	homebrew	xampp
   a2enmod support	yes	yes	no	no	no	no
   Modules to install	none
   Module name	n/a			dumpio
   Loadmodule directive	n/a			LoadModule dumpio_module <module_locations>/mod_dumpio.so

2. Open Apache's configuration file using your preferred text editor.

   $ sudo vi /etc/apache2/httpd.conf

   Configure the below steps/lines in a VirtualHost directive to apply the logging configuration only to a specific VirtualHost configuration.

   Related: Location for Apache VirtualHost configuration files

3. Turn on the related modules.

   DumpIOInput On
   DumpIOOutput On

4. Set the LogLevel to dumpio:trace7.

   LogLevel dumpio:trace7

   
5. Restart Apache for the changes to take effect.

   Related: How to manage Apache service

6. Create an HTTP POST request with dummy data in the request body to test.

   $ curl -XPOST --data "field01=value01&field02=value02" 127.0.0.1

7. Check Apache's error log to see the logged HTTP request body.

   $ sudo grep field01  /var/log/apache2/error.log
   [Sun Feb 02 01:46:13.062838 2020] [dumpio:trace7] [pid 21080] mod_dumpio.c(100): [client 127.0.0.1:47386] mod_dumpio:  dumpio_in (data-HEAP): field01=value01&field02=value02