Apache Cookbook, 2nd Edition

3.6. Logging Cookies

Problem

You want to record all the cookies sent to your server by clients and all the cookies your server asks clients to set in their databases; this can be useful when debugging Web applications that use cookies.

Solution

To log cookies received from the client:

CustomLog logs/cookies_in.log "%{UNIQUE_ID}e %{Cookie}i"
CustomLog logs/cookies2_in.log "%{UNIQUE_ID}e %{Cookie2}i"

To log cookie values set and sent by the server to the client:

CustomLog logs/cookies_out.log "%{UNIQUE_ID}e %{Set-Cookie}o"
CustomLog logs/cookies2_out.log "%{UNIQUE_ID}e %{Set-Cookie2}o"

In versions before to 2.0.56, using the %{Set-Cookie}o format effector for debugging is not recommended if multiple cookies are (or may be) involved. Only the first one will be recorded in the logfile. See the Discussion text for an example.

Discussion

Cookie fields tend to be very long and complex, so the previous statements will create separate files for logging them. The cookie log entries can be correlated against the client request access log using the server-set UNIQUE_ID environment variable (assuming that mod_unique_id is active in the server and that the activity log format includes the environment variable with a %{UNIQUE_ID}e format effector).

At the time of this writing, the Cookie and Set-Cookie header fields are most commonly used. The Cookie2 and corresponding Set-Cookie2 fields are newer and have been designed to correct some of the shortcomings in the original specifications, but they haven’t ...