NAME

Apache::AuthCookie - Perl Authentication and Authorization via cookies

SYNOPSIS

use mod_perl qw(1.07 StackedHandlers MethodHandlers Authen Authz);

=end html

# mod_perl startup script

use Sample::AuthCookieHandler;

# access.conf or .htaccess

<Location /unprotected/protected>
   PerlAuthenHandler Sample::AuthCookieHandler->authen
   PerlAuthzHandler Sample::AuthCookieHandler->authz
   AuthType Sample
   AuthName WhatEver
   PerlSetVar WhatEverPath /unprotected
   PerlSetVar WhatEverLoginScript /unprotected/login.pl
   require valid-user
</Location>

=end html

DESCRIPTION

Apache::AuthCookie allows you to intercept a users first unauthenticated access to a protected document. The user will be presented with a custom form where they can enter thier authentication credentials. The credentials are posted to the server where AuthCookie verifies them and generates a session key.

The session key is returned to the user's browser as a cookie. As a cookie, the browser will pass the session key on every subsequent accesses. AuthCookie will verify the session key and re-authenticate the user.

All you have to do is write a custom package that inheriets from AuthCookie. Your package implements two functions:

authen_cred()

Verify the credentials and return a session key.

authen_ses_key()

Verify the session key and return the user ID.

Using AuthCookie versus AuthBasic you get two key benefits.

1. The client doesn't *have* to pass the user credentials on every subsequent access. You have to do a little more work to get this feature, by having authen_cred() generate a session key.

2. When you determine that the client should stop using the credentials/session key, the server can tell the client to delete the cookie.

This is the flow of the authentication handler, less the details of the redirects. Two REDIRECT's are used to keep the client from displaying the user's credentials in the Location field. They don't really change AuthCookie's model, but they do add another round-trip request to the client.

(-----------------------)     +---------------------------------+
( Request a protected   )     | AuthCookie sets custom error    |
( page, but user hasn't )---->| document and returns            |
( authenticated (no     )     | AUTH_REQUIRED. Apache abandons  |      
( session key cookie)   )     | current request and creates sub |      
(-----------------------)     | request for the error document. |<-+
                              | Error document is a script that |  |
                              | generates a form where the user |  |
                return        | enters authentication           |  |
         ^------------------->| credentials (login & password). |  |
        / \      False        +---------------------------------+  |
       /   \                                   |                   |
      /     \                                  |                   |
     /       \                                 V                   |
    /         \               +---------------------------------+  |
   /   Pass    \              | User's client submits this form |  |
  /   user's    \             | to the same URL as the original |  |
  | credentials |<------------| request. AuthCookie sees that   |  |
  \     to      /             | the user isn't authenticated but|  |
   \authen_cred/              | this time there are credentials |  |
    \ function/               | as part of the request.         |  |
     \       /                +---------------------------------+  |
      \     /                                                      |
       \   /            +------------------------------------+     |
        \ /   return    | Authen cred returns an session     |  +--+
         V------------->| key which is opaque to AuthCookie.*|  |
               True     +------------------------------------+  |
                                             |                  |
              +--------------------+         |      +---------------+
              |                    |         |      | If we had a   |
              V                    |         V      | cookie, add   |
 +----------------------------+  r |         ^      | a Set-Cookie  |
 | If we didn't have a session|  e |T       / \     | header to     |
 | key cookie, add a          |  t |r      /   \    | override the  |
 | Set-Cookie header with this|  u |u     /     \   | invalid cookie|
 | session key. Client then   |  r |e    /       \  +---------------+
 | returns session key with   |  n |    /  pass   \               ^    
 | sucsesive requests         |    |   /  session  \              |    
 +----------------------------+    |  /   key to    \    return   |
              |                    +-| authen_ses_key|------------+
              V                       \             /     False
 +-----------------------------------+ \           /
 | Tell Apache to set Expires header |  \         /
 | set no-cache Pragma header, set   |   \       /
 | user to user ID returned by       |    \     /
 | authen_ses_key, set authentication|     \   /
 | to our type (e.g. AuthCookie).    |      \ /
 +-----------------------------------+       V
        (---------------------)              ^
        ( Request a protected )              |
        ( page, user has a    )--------------+
        ( session key cookie  )                    
        (---------------------)


*  The session key that the client gets can be anything you
   want. For example, encrypted information about the user, a
   hash of the username and password (similar in function to
   Digest authentication), or the user name and password in
   plain text (similar in function to HTTP Basic
   authentication).

   They only catch is that the authen_ses_key function that you
   create must be able to determine if this session_key is valid
   and map it back to the originally authenticated user ID.

EXAMPLE

Try the sample in eg/.

Install the sample

1. Install eg/Sample into the site_perl directory in your perl5 library directory.

2. Install eg/unprotected into your Apache document root directory.

3. Add use Sample::AuthCookieHandler; to your mod_perl startup script or Sample::AuthCookieHandler to your PerlModule configuration directive.

4. Restart Apache so mod_perl picks up Sample::AuthCookieHandler.

Tryout the sample

1. Try to access /unprotected/protected/get_me.html. You should instead get a form requesting a login and password. The sample will validate two users. The first is login => programmer and password => Hero and the second is login => some-user with no/any password. You might want to set your browser to show you cookies before accepting them. Then you can see what AuthCookie is generating.

2. As distributed, the .htaccess file in eg/unprotected/protected will allow either of these user to access the document. However if you change the line require valid-user to require dwarf in .htaccess only the user "programmer" will have access. Look at the authorization function dwarf() in eg/Sample/AuthCookieHandler.pm to see how this works.

Using a Session Key

Unlike the sample AuthCookieHandler, you have you verify the user's login and password in authen_cred(), then you do something like:

my $date = localtime;
my $ses_key = MD5->hexhash(join(';', $date, $PID, $PAC));

save $ses_key alogin with the user's login, and return $ses_key.

Now authen_ses_key() looks up the $ses_key passed to it and returns the saved login. I use Oracle to store the session key and retrieve it later, see the ToDo section below for some other ideas.

KNOWN LIMITATIONS

The first unauthenticated request can not be a POST. Apache::AuthCookie interupts the initial request with the form for the user credentials.

ToDo

• See if there's a way to allow the initial request to be a POST. I know Apache::AuthCookie could save the original POST'ed material but I don't know how to re-insert this content into the request stream after the user authenticates. If you knows of a way, please drop me a note.

• Create a session key store that uses shared memory. If anyone wants to get together and help with this that would be cool. Storing and retrieving them should be easy, but the harder part is cleaning out "old" keys and dealing with server restarts without losing all the keys.

AUTHOR

Eric Bartley, bartley@purdue.edu

SEE ALSO

perl(1), mod_perl(1), Apache(1).

cpanm Apache::AuthCookie

perl -MCPAN -e shell
install Apache::AuthCookie