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Apache2::ClickPath.3pm

NAME

Apache2::ClickPath - Apache WEB Server User Tracking

SYNOPSIS

  LoadModule perl_module ".../mod_perl.so"
  PerlLoadModule Apache2::ClickPath
  <ClickPathUAExceptions>
    Google     Googlebot
    MSN        msnbot
    Mirago     HeinrichderMiragoRobot
    Yahoo      Yahoo-MMCrawler
    Seekbot    Seekbot
    Picsearch  psbot
    Globalspec Ocelli
    Naver      NaverBot
    Turnitin   TurnitinBot
    dir.com    Pompos
    search.ch  search\.ch
    IBM        http://www\.almaden\.ibm\.com/cs/crawler/
  </ClickPathUAExceptions>
  ClickPathSessionPrefix "-S:"
  ClickPathMaxSessionAge 18000
  PerlTransHandler Apache2::ClickPath
  PerlOutputFilterHandler Apache2::ClickPath::OutputFilter
  LogFormat "%h %l %u %t \"%m %U%q %H\" %>s %b \"%{Referer}i\" \"%{User-agent}i\" \"%{SESSION}e\""
 
 

ABSTRACT

"Apache2::ClickPath" can be used to track user activity on your web server and gather click streams. Unlike mod_usertrack it does not use a cookie. Instead the session identifier is transferred as the first part on an URI.

Furthermore, in conjunction with a load balancer it can be used to direct all requests belonging to a session to the same server.

DESCRIPTION

"Apache2::ClickPath" adds a PerlTransHandler and an output filter to Apache's request cycle. The transhandler inspects the requested URI to decide if an existing session is used or a new one has to be created.

The Translation Handler

If the requested URI starts with a slash followed by the session prefix (see "ClickPathSessionPrefix" below) the rest of the URI up to the next slash is treated as session identifier. If for example the requested URI is "/-S:s9NNNd:doBAYNNNiaNQOtNNNNNM/index.html" then assuming "ClickPathSessionPrefix" is set to "-S:" the session identifier would be "s9NNNd:doBAYNNNiaNQOtNNNNNM".

Starting with version 1.8 a checksum is included in the session ID. Further, some parts of the information contained in the session including the checksum can be encrypted. This both makes a valid session ID hard to guess. If an invalid session ID is detected an error message is printed to the ErrorLog. So, a log watching agent can be set up to catch frequent abuses.

If no session identifier is found a new one is created.

Then the session prefix and identifier are stripped from the current URI. Also a potentially existing session is stripped from the incoming "Referer" header.

There are several exceptions to this scheme. Even if the incoming URI contains a session a new one is created if it is too old. This is done to prevent link collections, bookmarks or search engines generating endless click streams.

If the incoming "UserAgent" header matches a configurable regular expression neither session identifier is generated nor output filtering is done. That way search engine crawlers will not create sessions and links to your site remain readable (without the session stuff).

The translation handler sets the following environment variables that can be used in CGI programms or template systems (eg. SSI):

SESSION

the session identifier itself. In the example above "s9NNNd:doBAYNNNiaNQOtNNNNNM" is assigned. If the "UserAgent" prevents session generation the name of the matching regular expression is assigned, (see "ClickPathUAExceptions").

CGI_SESSION

the session prefix + the session identifier. In the example above "/-S:s9NNNd:doBAYNNNiaNQOtNNNNNM" is assigned. If the "UserAgent" prevents session generation "CGI_SESSION" is empty.

SESSION_START

the request time of the request starting a session in seconds since 1/1/1970.

CGI_SESSION_AGE

the session age in seconds, i.e. CURRENT_TIME - SESSION_START.

REMOTE_SESSION

in case a friendly session was caught this variable contains it, see below.

REMOTE_SESSION_HOST

in case a friendly session was caught this variable contains the host it belongs to, see below.

EXPIRED_SESSION

if a session has expired and a new one has been created the old session is stored here.

INVALID_SESSION

when a "ClickPathMachineTable" is used a check is accomplished to ensure the session was created by on of the machines of the cluster. If it was not a message is written to the "ErrorLog", a new one is created and the invalid session is written to this environment variable.

ClickPathMachineName

when a "ClickPathMachineTable" is used this variable contains the name of the machine where the session has been created.

ClickPathMachineStore

when a "ClickPathMachineTable" is used this variable contains the address of the session store in terms of "Apache2::ClickPath::Store".

The Output Filter

The output filter is entirely skipped if the translation handler had not set the "CGI_SESSION" environment variable.

It prepends the session prefix and identifier to any "Location" an "Refresh" output headers.

If the output "Content-Type" is "text/html" the body part is modified. In this case the filter patches the following HTML tags:

<a ... href="LINK" ...>

<area ... href="LINK" ...>

<form ... action="LINK" ...>

<frame ... src="LINK" ...>

<iframe ... src="LINK" ...>

<meta ... http-equiv="refresh" ... content="N; URL=LINK" ...>

In all cases if "LINK" starts with a slash the current value of "CGI_SESSION" is prepended. If "LINK" starts with "http://HOST/" (or https:) where "HOST" matches the incoming "Host" header "CGI_SESSION" is inserted right after "HOST". If "LINK" is relative and the incoming request URI had contained a session then "LINK" is left unmodified. Otherwize it is converted to a link starting with a slash and "CGI_SESSION" is prepended.

Configuration Directives

All directives are valid only in server config or virtual host contexts.

ClickPathSessionPrefix

specifies the session prefix without the leading slash.

ClickPathMaxSessionAge

if a session gets older than this value (in seconds) a new one is created instead of continuing the old. Values of about a few hours should be good, eg. 18000 = 5 h.

ClickPathMachine

set this machine's name. The name is used with load balancers. Each machine of a farm is assigned a unique name. That makes session identifiers unique across the farm.

If this directive is omitted a compressed form (6 Bytes) of the server's IP address is used. Thus the session is unique across the Internet.

In environments with only one server this directive can be given without an argument. Then an empty name is used and the session is unique on the server.

If possible use short or empty names. It saves bandwidth.

A name consists of letters, digits and underscores (_).

The generated session identifier contains the name in a slightly scrambled form to slightly hide your infrastructure.

ClickPathMachineTable

this is a container directive like "<Location>" or "<Directory>". It defines a 3-column table specifying the layout of your WEB-server cluster. Each line consists of max. 3 fields. The 1st one is the IP address or name the server is listening on. Second comes an optional machine name in in terms of the "ClickPathMachine" directive. If it is omitted each machine is assigned it's line number within the table as name. This means that each machine in a cluster must run with exactly the same table regarding the line order. The optional 3rd field specifies the address where the session store is accessible (see Apache2::ClickPath::Store for more information.

ClickPathUAExceptions

this is a container directive like "<Location>" or "<Directory>". The container content lines consist of a name and a regular expression. For example

  1   <ClickPathUAExceptions>
  2     Google     Googlebot
  3     MSN        (?i:msnbot)
  4   </ClickPathUAExceptions>
 
 

Line 2 maps each "UserAgent" containing the word "Googlebot" to the name "Google". Now if a request comes in with an "UserAgent" header containing "Googlebot" no session is generated. Instead the environment variable "SESSION" is set to "Google" and "CGI_SESSION" is emtpy.

ClickPathUAExceptionsFile

this directive takes a filename as argument. The file's syntax and semantic are the same as for "ClickPathUAExceptions". The file is reread every time is has been changed avoiding server restarts after configuration changes at the prize of memory consumption.

ClickPathFriendlySessions

this is also a container directive. It describes friendly sessions. What is a friendly session? Well, suppose you have a WEB shop running on "shop.tld.org" and your company site running on "www.tld.org". The shop does it's own URL based session management but there are links from the shop to the company site and back. Wouldn't it be nice if a customer once he has stepped into the shop could click links to the company without loosing the shopping session? This is where friendly sessions come in.

Since your shop's session management is URL based the "Referer" seen by "www.tld.org" will be something like

  https://shop.tld.org/cgi-bin/shop.pl?session=sdafsgr;clusterid=25
 
 

(if session and clusterid are passed as CGI parameters) or

  https://shop.tld.org/C:25/S:sdafsgr/cgi-bin/shop.pl
 
 

(if session and clusterid are passed as URL parts) or something mixed.

Assuming that "clusterid" and "session" both identify the session on "shop.tld.org" "Apache2::ClickPath" can extract them, encode them in it's own session and place them in environment variables.

Each line in the "ClickPathFriendlySessions" section decribes one friendly site. The line consists of the friendly hostname, a list of URL parts or CGI parameters identifying the friendly session and an optional short name for this friend, eg:

  shop.tld.org uri(1) param(session) shop
 
 

This means sessions at "shop.tld.org" are identified by the combination of 1st URL part after the leading slash (/) and a CGI parameter named "session".

If now a request comes in with a "Referer" of "http://shop.tld.org/25/bin/shop.pl?action=showbasket;session=213" the "REMOTE_SESSION" environment variable will contain 2 lines:

  25
  session=213
 
 

Their order is determined by the order of "uri()" and "param()" statements in the configuration section between the hostname and the short name. The "REMOTE_SESSION_HOST" environment variable will contain the host name the session belongs to.

Now a CGI script or a modperl handler or something similar can fetch the environment and build links back to "shop.tld.org". Instead of directly linking back to the shop your links then point to that script. The script then puts out an appropriate redirect.

ClickPathFriendlySessionsFile

this directive takes a filename as argument. The file's syntax and semantic are the same as for "ClickPathFriendlySessions". The file is reread every time is has been changed avoiding server restarts after configuration changes at the prize of memory consumption.

ClickPathSecret

ClickPathSecretIV

if you want to run something like a shop with our session identifiers they must be unguessable. That means knowing a valid session ID it must be difficult to guess another one. With these directives a significant part of the session ID is encrypted with Blowfish in the cipher block chaining mode thus making the session ID unguessable. "ClickPathSecret" specifies the key, "ClickPathSecretIV" the initialization vector.

"ClickPathSecretIV" is a simple string of arbitrary length. The first 8 bytes of its MD5 digest are used as initialization vector. If omitted the string "abcd1234" is the IV.

"ClickPathSecret" is given as "http:", "https:", "file:" or "data:" URL. Thus the secret can be stored directly as data-URL in the httpd.conf or in a separate file on the local disk or on a possibly secured server. To enable all modes of accessing the WEB the http(s)-URL syntax is a bit extented. Maybe you have already used "http://user:password@server.tld/...". Many browsers allow this syntax to specify a username and password for HTTP authentication. But how about proxies, SSL-authentication etc? Well, add another colon (:) after the password and append a semicolon (;) delimited list of "key=value" pairs. The special characters (@:;\) can be quoted with a backslash (\). In fact, all characters can be quoted. Thus, "\a" and "a" produce the same string "a".

The following keys are defined:

https_proxy

https_proxy_username

https_proxy_password

https_version

https_cert_file

https_key_file

https_ca_file

https_ca_dir

https_pkcs12_file

https_pkcs12_password

their meaning is defined in Crypt::SSLeay.

http_proxy

http_proxy_username

http_proxy_password

these are passed to LWP::UserAgent.

Remember a HTTP-proxy is accessed with the GET or POST, ... methods whereas a HTTPS-proxy is accessed with CONNECT. Don't mix them, see Crypt::SSLeay.

Examples

  ClickPathSecret https://john:a\@b\;c\::https_ca_file=/my/ca.pem@secrethost.tld/bin/secret.pl?host=me
 
 

fetches the secret from "https://secrethost.tdl/bin/secret.pl?host=me" using "john" as username and "a@b;c:" as password. The server certificate of secrethost.tld is verified against the CA certificate found in "/my/ca.pem".

  ClickPathSecret https://::https_pkcs12_file=/my/john.p12;https_pkcs12_password=a\@b\;c\:;https_ca_file=/my/ca.pem@secrethost.tld/bin/secret.pl?host=me
 
 

fetches the secret again from "https://secrethost.tdl/bin/secret.pl?host=me" using "/my/john.p12" as client certificate with "a@b;c:" as password. The server certificate of secrethost.tld is again verified against the CA certificate found in "/my/ca.pem".

  ClickPathSecret data:,password:very%20secret%20password
 
 

here a data-URL is used that produces the content "password:very secret password".

The URL's content is fetched by LWP::UserAgent once at server startup.

Its content defines the secret either in binary form or as string of hexadecimal characters or as a password. If it starts with "binary:" the rest of the content is taken as is as the key. If it starts with "hex:" "pack( 'H*', $arg )" is used to convert it to binary. If it starts with "password:" or with neither of them the MD5 digest of the rest of the content is used as secret.

The Blowfish algorithm allows up to 56 bytes as secret. In hex and binary mode the starting 56 bytes are used. You can specify more bytes but they won't be regarded. In password mode the MD5 algorithm produces 16 bytes long secret.

Working with a load balancer

Most load balancers are able to map a request to a particular machine based on a part of the request URI. They look for a prefix followed by a given number of characters or until a suffix is found. The string between identifies the machine to route the request to.

The name set with "ClickPathMachine" can be used by a load balancer. It is immediately following the session prefix and finished by a single colon. The default name is always 6 bytes long.

Logging

The most important part of user tracking and clickstreams is logging. With "Apache2::ClickPath" many request URIs contain an initial session part. Thus, for logfile analyzers most requests are unique which leads to useless results. Normally Apache's common logfile format starts with

  %h %l %u %t \"%r\"
 
 

%r stands for the request. It is the first line a browser sends to a server. For use with "Apache2::ClickPath" %r is better changed to "%m %U%q %H". Since "Apache2::ClickPath" strips the session part from the current URI %U appears without the session. With this modification logfile analyzers will produce meaningful results again.

The session can be logged as "%{SESSION}e" at end of a logfile line.

A word about proxies

Depending on your content and your users community HTTP proxies can serve a significant part of your traffic. With "Apache2::ClickPath" almost all request have to be served by your server.

Debugging

Sometimes it is useful to know the information encoded in a session identifier. This is why Apache2::ClickPath::Decode exists.

SEE ALSO

Apache2::ClickPath::Store Apache2::ClickPath::StoreClient Apache2::ClickPath::Decode <http://perl.apache.org>, <http://httpd.apache.org>

AUTHOR

Torsten Foertsch, <torsten.foertsch@gmx.net>

COPYRIGHT AND LICENSE

Copyright (C) 2004-2005 by Torsten Foertsch

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.