Michael Schout > Apache-AuthTicket > Apache2::AuthTicket

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Module Version: 0.93   Source  

NAME ^

Apache2::AuthTicket - Cookie Based Access and Authorization Module

VERSION ^

version 0.93

SYNOPSIS ^

 # in httpd.conf
 PerlModule Apache2::AuthTicket
 PerlSetVar FooTicketDB DBI:mysql:database=mschout;host=testbed
 PerlSetVar FooTicketDBUser test
 PerlSetVar FooTicketDBPassword secret
 PerlSetVar FooTicketTable tickets:ticket_hash:ts
 PerlSetVar FooTicketUserTable myusers:usename:passwd
 PerlSetVar FooTicketPasswordStyle cleartext
 PerlSetVar FooTicketSecretTable ticket_secrets:sec_data:sec_version
 PerlSetVar FooTicketExpires 15
 PerlSetVar FooTicketLogoutURI /foo/index.html
 PerlSetVar FooTicketLoginHandler /foologin
 PerlSetVar FooTicketIdleTimeout 1
 PerlSetVar FooPath /
 PerlSetVar FooDomain .foo.com
 PerlSetVar FooSecure 1
 PerlSetVar FooLoginScript /foologinform

 <Location /foo>
     AuthType Apache2::AuthTicket
     AuthName Foo
     PerlAuthenHandler Apache2::AuthTicket->authenticate
     PerlAuthzHandler Apache2::AuthTicket->authorize
     require valid-user
 </Location>
 
 <Location /foologinform>
     AuthType Apache2::AuthTicket
     AuthName Foo
     SetHandler perl-script
     PerlResponseHandler Apache2::AuthTicket->login_screen
 </Location>
 
 <Location /foologin>
     AuthType Apache2::AuthTicket
     AuthName Foo
     SetHandler perl-script
     PerlResponseHandler Apache2::AuthTicket->login
 </Location>
 
 <Location /foo/logout>
     AuthType Apache2::AuthTicket
     AuthName Foo
     SetHandler perl-script
     PerlResponseHandler Apache2::AuthTicket->logout
 </Location>

DESCRIPTION ^

This module provides ticket based access control. The theory behind this is similar to the system described in the eagle book.

This module works using HTTP cookies to check if a user is authorized to view a page. Apache2::AuthCookie is used as the underlying mechanism for managing cookies.

This module was designed to be as extensible as possible. Its quite likely that you will want to create your own subclass of Apache2::AuthTicket in order to customize various aspects of this module (show your own versions of the forms, override database methods etc).

This system uses cookies to authenticate users. When a user is authenticated through this system, they are issued a cookie consisting of the time, the username of the user, the expriation time of the cookie, a "secret" version (described later), and a cryptographic signature. The cryptographic signature is generated using the MD5 algorithm on the cookie data and a "secret" key that is read from a database. Each secret key also has a version number associated with it. This allows the site administrator to issue a new secret periodically without invalidating the current valid tickets. For example, the site administrator might periodically insert a new secret key into the databse periodically, and flush secrets that are more than 2 days old. Since the ticket issued to the user contains the secret version, the authentication process will still allow tickets to be authorized as long as the corresponding secrets exist in the ticket secrets table.

The actual contents and length of secret data is left to the site administrator. A good choice might be to read data from /dev/random, unpack it into a hex string and save that.

This system should be reasonably secure becuase the IP address of the end user is incorporated into the cryptographic signature. If the ticket were intercepted, then an attacker would have to steal the user's IP address in order to be able to use the ticket. Plus, since the tickets can expire automatically, we can be sure that the ticket is not valid for a long period of time. Finally, by using the Secure mode of Apache2::AuthCookie, the ticket is not passed over unencrypted connections. In order to attack this system, an attacker would have to exploit both the MD5 algorightm as well as SSL. Chances are, by the time the user could break both of these, the ticket would no longer be valid.

CONFIGURATION ^

There are two things you must do in order to configure this module:

 1) configure your mod_perl apache server
 2) create the necessary database tables.

Apache Configuration - httpd.conf

There are two ways that this module could be configured. Either by using a function call in startup.pl, or by configuring each handler explicitly in httpd.conf. If you decide to mix and match using calls to Apache2::AuthTicket->configure() with directives in httpd.conf, then remember that the following precedence applies:

 o If a directive is specified in httpd.conf, it will be used.
 o else if a directive is specified by configure(), then the 
   configure() value will be used.
 o else a default value will be used.

Default values are subject to change in later versions, so you are better of explicitly configuring all values and not relying on any defaults.

There are four blocks that need to be entered into httpd.conf. The first of these is the block specifying your access restrictions. This block should look somrthing like this:

 <Location /foo>
     AuthType Apache2::AuthTicket
     AuthName Foo
     PerlAuthenHandler Apache2::AuthTicket->authenticate
     PerlAuthzHandler Apache2::AuthTicket->authorize
     require valid-user
 </Location>

The remaining blocks control how to display the login form, and the login and logout urls. These blocks should look similar to this:

 <Location /foologinform>
     AuthType Apache2::AuthTicket
     AuthName Foo
     SetHandler perl-script
     PerlResponseHandler Apache2::AuthTicket->login_screen
 </Location>
 
 <Location /foologin>
     AuthType    Apache2::AuthTicket
     AuthName    Foo
     SetHandler  perl-script
     PerlResponseHandler Apache2::AuthTicket->login
 </Location>
 
 <Location /foo/logout>
     AuthType Apache2::AuthTicket
     AuthName Foo
     SetHandler perl-script
     PerlResponseHandler Apache2::AuthTicket->logout
 </Location>

Apache Configuration - startup.pl

Any Apache2::AuthTicket configuration items can be set in startup.pl. You can configure an AuthName like this:

 Apache2::AuthTicket->configure(String auth_name, *Hash config)

Note that when configuring this way you dont prefix the configuration items with the AuthName value like you do when using PerlSetVar directives.

Note: You must still include Apache2::AuthCookie configuration directives in httpd.conf when configuring the server this way. These items include:

    PerlSetVar FooPath /
    PerlSetVar FooDomain .foo.com
    PerlSetVar FooSecure 1
    PerlSetVar FooLoginScript /foologinform

example: Apache2::AuthTicket->configure('Foo', { TicketDB => 'DBI:mysql:database=test;host=foo', TicketDBUser => 'mschout', TicketDBPassword => 'secret', TicketTable => 'tickets:ticket_hash:ts', TicketUserTablei => 'myusers:usename:passwd', TicketPasswordStyle => 'cleartext', TicketSecretTable => 'ticket_secrets:sec_data:sec_version', TicketExpires => '15', TicketLogoutURI => '/foo/index.html', TicketLoginHandler => '/foologin', TicketIdleTimeout => 5 });

Valid configuration items are:

TicketDB

This directive specifys the DBI URL string to use when connecting to the database. Also, you might consider overloading the dbi_connect method to handle setting up your db connection if you are creating a subclass of this module.

example: dbi:Pg:dbname=test

TicketDBUser

This directive specifys the username to use when connecting to the databse.

TicketDBPassword

This directive specifys the password to use when connecting to the databse.

TicketTable

This directive specifys the ticket hash table as well as the column name for the hash.

Format: table_name:ticket_column_name:timestamp_column

Example: tickets:ticket_hash:ts

TicketUserTable

This directive specifys the users table and the username and password column names.

Format: table_name:username_column:password_column

Example: users:usrname:passwd

TicketPasswordStyle

This directive specifys what type of passwords are stored in the database. The default is to use cleartext passwords. Currently supported password styles are:

cleartext

This password style is just plain text passwords. When using this password style, the supplied user password is simply compared with the password stored in the database.

md5

This password style generates an MD5 hex hash of the supplied password before comparing it against the password stored in the database. Passwords should be stored in the database by passing them through Digest::MD5::md5_hex().

crypt

This password style uses traditional crypt() to encrypt the supplied password before comparing it to the password saved in the database.

TicketSecretTable

This directive specifys the server secret table as well as the names of the secret data column and the version column.

Format: table_name:data_column:version_column

Example: ticketsecrets:sec_data:sec_version

TicketExpires

This directive specifys the number of minutes that tickets should remain valid for. If a user exceeds this limit, they will be forced to log in again.

This should not be confused with the inherited AuthCookie setting Expire, which is the cookie expiration time. TicketExpires controls the expiration of the ticket, not the cookie.

TicketIdleTimeout

This directive specifys the number of minutes of inactivity before a ticket is considered invalid. Setting this value to 5 for example would force a re-login if no requests are recieved from the user in a 5 minute period.

The default for this value is 0, which disables this feature. If this number is larger than TicketExpires, then this setting will have no effect.

TicketLogoutURI

This directive specifys the URL that the user should be sent to after they are successfully logged out (this is done via a redirect).

Example: /logged_out_message.html

TicketCheckIP (default: on)

This controlls whether or not the client IP address is included in the ticket hash. The default is 'on'. If you turn this off, then the client ip address will not be checked. It is sometimes not desirable to check the client ip if the clients are behind load balancers and subsequent requests might come in from a different IP.

TicketCheckBrowser (default: off)

This controlls whether or not the USER_AGENT string is included in the ticket hash. This can be used in conjunction with, or instead of TicketCheckIP to prevent tampering with the ticket.

Database Configuration

Three database tables are needed for this module:

users table

This table stores the actual usernames and passwords of the users. This table needs to contain at least a username and password column. This table is confgured by the TicketUserTable directive.

 example:

 CREATE TABLE users (
     usename VARCHAR(32) NOT NULL,
     passwd  VARCHAR(32) NOT NULL
 );
tickets table

This table stores the ticket hash for each ticket. This information must be stored locally so that users can be forcefully logged out without worrying if the HTTP cookie doesn't get deleted.

 example:

 CREATE TABLE tickets (
    ticket_hash CHAR(32) NOT NULL,
    ts          INT NOT NULL,
    PRIMARY KEY (ticket_hash)
 );
secrets table

This table contains the server secret and a numeric version for the secret. This table is configured by the TicketSecretTable directive.

 example:

 CREATE TABLE ticketsecrets (
     sec_version  SERIAL,
     sec_data     TEXT NOT NULL
 );

METHODS ^

This is not a complete listing of methods contained in Apache2::AuthTicket. Rather, it is a listing of methods that you might want to overload if you were subclassing this module. Other methods that exist in the module are probably not useful to you.

Feel free to examine the source code for other methods that you might choose to overload.

void make_login_screen($r, String action, String destination)

This method creats the "login" screen that is shown to the user. You can overload this method to create your own login screen. The log in screen only needs to contain a hidden field called "destination" with the contents of destination in it, a text field named credential_0 and a password field named credential_1. You are responsible for sending the http header as well as the content. See Apache2::AuthCookie for the description of what each of these fields are for.

action contains the action URL for the form. You must set the action of your form to this value for it to function correctly.

Apache2::AuthTicket also provides a mechanism to determine why the login for is being displayed. This can be used in conjunction with Apache2::AuthCookie's "AuthCookieReason" setting to determine why the user is being asked to log in. Apache2::AuthCookie sets $r->prev->subprocess_env("AuthCookieReason") to either "no_cookie" or "bad_cookie" when this page is loaded. If the value is "no_cookie" then the user is being asked to log in for the first time, or they are logging in after they previously logged out. If this value is "bad_cookie" then Apache2::AuthTicket is asking them to re-login for some reason. To determine what this reason is, you must examine $r->prev->subprocess_env("AuthTicketReason"). AuthTicketReason can take the following values:

malformed_ticket

This value means that the ticket is malformed. In other words, the ticket does not contain all of the required information that should be present.

invalid_hash

This value means that the hash contained in the ticket does not match any values in the tickets database table. This might happen if you are periodically clearing out old tickets from the database and the user presents a ticket that has been deleted.

expired_ticket

This value means that the ticket has expired and the user must re-login to be issued a new ticket.

missing_secret

This value means that the server secret could not be loaded.

idle_timeout

This value means that the user has exceeded the TicketIdleTimeout minutes of inactivity, and the user must re-login.

tampered_hash

This value indicates that the ticket data does not match its cryptographic signature, and the ticket has most likely been tampered with. The user is forced to re-login at this point.

You can use these values in your make_login_screen() method to display a message stating why the user must login (e.g.: "you have exceeded 5 minutes of inactivity and you must re-login").

DBI::db dbi_connect()

This method connects to the TicketDB data source. You might overload this method if you have a common DBI connection function. For example:

 sub dbi_connect {
     my ($self) = @_;
     return Foo::dbi_connect();
 }

Note that you can also adjust the DBI connection settings by setting TicketDB, TicketDBUser, and TicketDBPassword in httpd.conf.

CREDITS ^

The idea for this module came from the Ticket Access system in the eagle book, along with several ideas discussed on the mod_perl mailing list.

SEE ALSO ^

perl, mod_perl, Apache2::AuthCookie

SOURCE ^

The development version is on github at http://github.com/mschout/apache-authticket and may be cloned from git://github.com/mschout/apache-authticket.git

BUGS ^

Please report any bugs or feature requests to bug-apache-authticket@rt.cpan.org or through the web interface at: http://rt.cpan.org/Public/Dist/Display.html?Name=Apache-AuthTicket

AUTHOR ^

Michael Schout <mschout@cpan.org>

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2000 by Michael Schout.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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