NAME
Apache::AuthCookie - Perl Authentication and Authorization via cookies
SYNOPSIS
`use mod_perl qw(1.07 StackedHandlers MethodHandlers Authen Authz);'
# In httpd.conf or .htaccess:
PerlModule Sample::AuthCookieHandler
PerlSetVar WhatEverPath /
PerlSetVar WhatEverLoginScript /login.pl
# These documents require user to be logged in.
<Location /protected>
AuthType Sample
AuthName WhatEver
PerlAuthenHandler Sample::AuthCookieHandler->authenticate
PerlAuthzHandler Sample::AuthCookieHandler->authorize
require valid-user
</Location>
# These documents don't require logging in, but allow it.
<FilesMatch "\.ok$">
AuthType Sample
AuthName WhatEver
PerlFixupHandler Sample::AuthCookieHandler->recognize_user
</FilesMatch>
# This is the action of the login.pl script above.
<Files LOGIN>
AuthType Sample
AuthName WhatEver
SetHandler perl-script
PerlHandler Sample::AuthCookieHandler->login
</Files>
DESCRIPTION
Apache::AuthCookie allows you to intercept a user's first
unauthenticated access to a protected document. The user will be
presented with a custom form where they can enter authentication
credentials. The credentials are posted to the server where AuthCookie
verifies them and returns a session key.
The session key is returned to the user's browser as a cookie. As a
cookie, the browser will pass the session key on every subsequent
accesses. AuthCookie will verify the session key and re-authenticate the
user.
All you have to do is write a custom module that inherits from
AuthCookie. Your module implements two functions:
`authen_cred()'
Verify the user-supplied credentials and return a session key. The
session key can be any string - often you'll use some string
containing username, timeout info, and any other information you
need to determine access to documents, and append a one-way hash of
those values together with some secret key.
`authen_ses_key()'
Verify the session key (previously generated by `authen_cred()',
possibly during a previous request) and return the user ID. This
user ID will be fed to `$r->connection->user()' to set Apache's idea
of who's logged in.
By using AuthCookie versus Apache's built-in AuthBasic you can design
your own authentication system. There are at least three main benefits.
1. The client doesn't *have* to pass the user credentials on every
subsequent access. If you're using passwords, this means that the
password can be sent on the first request only, and subsequent
requests don't need to send this (potentially sensitive)
information. This is known as "ticket-based" authentication.
2. When you determine that the client should stop using the
credentials/session key, the server can tell the client to delete
the cookie. Letting users "log out" is a notoriously impossible-to-
solve problem of AuthBasic.
3. AuthBasic dialog boxes are ugly. You can design your own HTML login
forms when you use AuthCookie.
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 LOGIN URL, which calls | |
| credentials |<------------| AuthCookie->login(). | |
\ to / +---------------------------------+ |
\authen_cred/ |
\ function/ |
\ / |
\ / |
\ / +------------------------------------+ |
\ / return | Authen cred returns a 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).
The only requirement 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.
UPGRADING FROM VERSION 1.4
There are a few interface changes that you need to be aware of when
migrating from version 1.x to 2.x. First, the authen() and authz()
methods are now deprecated, replaced by the new authenticate() and
authorize() methods. The old methods will go away in a couple versions,
but are maintained intact in this version to ease the task of upgrading.
The use of these methods is essentially the same, though.
Second, when you change to the new method names (see previous
paragraph), you must change the action of your login forms to the
location /LOGIN (or whatever URL will call your module's login()
method). You may also want to change their METHOD to POST instead of
GET, since that's much safer and nicer to look at (but you can leave it
as GET if you bloody well want to, for some god-unknown reason).
Third, you must change your login forms (see the section on "THE LOGIN
SCRIPT" below) to indicate how requests should be redirected after a
successful login.
Fourth, you might want to take advantage of the new `logout()' method,
though you certainly don't have to.
EXAMPLE
For an example of how to use Apache::AuthCookie, you may want to check
out the test suite, which runs AuthCookie through a few of its paces.
The documents are located in t/eg/, and you may want to peruse t/real.t
to see the generated httpd.conf file (at the bottom of real.t) and check
out what requests it's making of the server (at the top of real.t).
THE LOGIN SCRIPT
You will need to create a login script (called login.pl above) that
generates an HTML form for the user to fill out. The following fields
must be present in the form:
1. The ACTION of the form must be /LOGIN (or whatever you defined in your
server configuration, as in the SYNOPSIS section).
2. The various user input fields (username, passwords, etc.) must be named
'credential_0', 'credential_1', etc. on the form.
3. You must define a form field called 'destination' that tells AuthCookie
where to redirect the request after successfully logging in.
Typically this value is obtained from `$r->prev->uri'. See the
login.pl script in t/eg/.
THE LOGOUT SCRIPT
If you want to let users log themselves out (something that can't be
done using Basic Auth), you need to create a logout script. For an
example, see t/eg/logout.pl. Logout scripts may want to take advantage
of AuthCookie's `logout()' method, which will set the proper cookie
headers in order to clear the user's cookie.
Note that if you don't necessarily trust your users, you can't count on
cookie deletion for logging out. You'll have to expire some server-side
login information too. AuthCookie doesn't do this for you, you have to
handle it yourself.
ABOUT SESSION KEYS
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' along 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
If the first unauthenticated request is a POST, it will be changed to a
GET after the user fills out the login forms, and POSTed data will be
lost.
TO DO
* There ought to be a way to solve the GET/POST problems in the
LIMITATIONS section. They both involve being able to change a
request back & forth between GET & POST. The second problem also
involves being able to re-insert the POSTed content into the request
stream after the user authenticates. If you knows of a way, please
drop me a note.
It might be nice if the logout method could accept some parameters
that could make it easy to redirect the user to another URI, or
whatever. I'd have to think about the options needed before I
implement anything, though.
AUTHOR
Ken Williams, ken@forum.swarthmore.edu
Originally written by Eric Bartley, bartley@purdue.edu
SEE ALSO
the perl(1) manpage, the mod_perl(1) manpage, the Apache(1) manpage.