Is it possible to exclude specified GET parameters in apache access logs?

Question

I need to exclude some sensitive details in my apache log, but I want to keep the log and the uri's in it. Is it possible to achieve following in my access log:

127.0.0.1 - - [27/Feb/2012:13:18:12 +0100] "GET /api.php?param=secret HTTP/1.1" 200 7600 "http://localhost/api.php" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11"

I want to replace "secret" with "[FILTERED]" like this:

127.0.0.1 - - [27/Feb/2012:13:18:12 +0100] "GET /api.php?param=[FILTERED] HTTP/1.1" 200 7600 "http://localhost/api.php" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11"

I know I probably should have used POST to send this variable, but the damage is already done. I've looked at http://httpd.apache.org/docs/2.4/logs.html and LogFormat, but could not find any possibilities to use regular expression or similar. Any suggestions?

[edit]

Do NOT send sensitive variables as GET parameters if you have the possibility to choose.

Answer 1

I've found one way to solve the problem. If I pipe the log output to sed, I can perform a regex replace on the output before I append it to the log file.

Example 1

CustomLog "|/bin/sed -E s/'param=[^& \t\n]*'/'param=\[FILTERED\]'/g >> /your/path/access.log" combined

Example 2

It's also possible to exclude several parameters:

exclude.sh

#!/bin/bash
while read x ; do
    result=$x
    for ARG in "$@"
    do
        cleanArg=`echo $ARG | sed -E 's|([^0-9a-zA-Z_])|\\\\\1|g'`
        result=`echo $result | sed -E s/$cleanArg'=[^& \t\n]*'/$cleanArg'=\[FILTERED\]'/g`
    done
    echo $result
done

Move the script above to the folder /opt/scripts/ or somewhere else, give the script execute rights (chmod +x exclude.sh) and modify your apache config like this:

CustomLog "|/opt/scripts/exclude.sh param param1 param2 >> /your/path/access.log" combined

Documentation

http://httpd.apache.org/docs/2.4/logs.html#piped

http://www.gnu.org/software/sed/manual/sed.html