man Apache2_4::AuthCookie (3): Perl Authentication and Authorization via cookies for Apache 2.4

VERSION

version 3.24

SYNOPSIS

Make sure your mod_perl is at least 2.0.9, with StackedHandlers, MethodHandlers, Authen, and Authz compiled in.

# In httpd.conf or .htaccess:
PerlModule Sample::Apache2::AuthCookieHandler
PerlSetVar WhatEverPath /
PerlSetVar WhatEverLoginScript /login.pl
# The following line is optional - it allows you to set the domain
# scope of your cookie. Default is the current domain.
PerlSetVar WhatEverDomain .yourdomain.com
# Use this to only send over a secure connection
PerlSetVar WhatEverSecure 1
# Use this if you want user session cookies to expire if the user
# doesn't request a auth-required or recognize_user page for some
# time period. If set, a new cookie (with updated expire time)
# is set on every request.
PerlSetVar WhatEverSessionTimeout +30m
# to enable the HttpOnly cookie property, use HttpOnly.
# this is an MS extension. See:
# http://msdn.microsoft.com/workshop/author/dhtml/httponly_cookies.asp
PerlSetVar WhatEverHttpOnly 1
# Usually documents are uncached - turn off here
PerlSetVar WhatEverCache 1
# Use this to make your cookies persistent (+2 hours here)
PerlSetVar WhatEverExpires +2h
# Use to make AuthCookie send a P3P header with the cookie
# see http://www.w3.org/P3P/ for details about what the value
# of this should be
PerlSetVar WhatEverP3P "CP=\"...\""
# These documents require user to be logged in.
<Location /protected>
AuthType Sample::Apache2::AuthCookieHandler
AuthName WhatEver
PerlAuthenHandler Sample::Apache2::AuthCookieHandler->authenticate
Require valid-user
</Location>
# How to handle a custom requirement (non-user).
PerlAddAuthzProvider species Sample::Apache2::AuthCookieHandler->authz_species
<Location /protected/species>
Require species klingon
</Location>
# These documents don't require logging in, but allow it.
<FilesMatch "\.ok$">
AuthType Sample::Apache2::AuthCookieHandler
AuthName WhatEver
PerlFixupHandler Sample::Apache2::AuthCookieHandler->recognize_user
</FilesMatch>
# This is the action of the login.pl script above.
<Files LOGIN>
AuthType Sample::Apache2::AuthCookieHandler
AuthName WhatEver
SetHandler perl-script
PerlResponseHandler Sample::Apache2::AuthCookieHandler->login
</Files>

DESCRIPTION

This module is for "mod_perl" version 2 for "Apache" version 2.4.x. If you are running mod_perl version 1, you need Apache::AuthCookie instead. If you are running "Apache" 2.0.0-2.2.x, you need Apache2::AuthCookie instead.

Apache2_4::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 is a class which implements two methods:

"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->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 several 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.

4.

You can specify the domain of a cookie using "PerlSetVar" commands. For instance, if your AuthName is "WhatEver", you can put the command

 PerlSetVar WhatEverDomain .yourhost.com

into your server setup file and your access cookies will span all hosts ending in ".yourhost.com".

5.

You can optionally specify the name of your cookie using the "CookieName" directive. For instance, if your AuthName is "WhatEver", you can put the command

 PerlSetVar WhatEverCookieName MyCustomName

into your server setup file and your cookies for this AuthCookie realm will be named MyCustomName. Default is AuthType_AuthName.

This is the flow of the authentication handler, less the details of the redirects. Two HTTP_MOVED_TEMPORARILY'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     )     | HTTP_FORBIDDEN. 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   \               ^    
  | successive requests        |    |   /  session  \              |
  +----------------------------+    |  /   key to    \    return   |
               |                    +-| authen_ses_key|------------+
               V                       \             /     False
  +-----------------------------------+ \           /
  | Tell Apache to set Expires 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.

METHODS

"Apache2_4::AuthCookie" has several methods you should know about.

authenticate()
This method is one you'll use in a server config file (httpd.conf, .htaccess, ...) as a PerlAuthenHandler. If the user provided a session key in a cookie, the "authen_ses_key()" method will get called to check whether the key is valid. If not, or if there is no key provided, we redirect to the login form.
authen_cred()
You must define this method yourself in your subclass of "Apache2_4::AuthCookie". Its job is to create the session key that will be preserved in the user's cookie. The arguments passed to it are:
```
 sub authen_cred ($$\@) {
     my $self = shift;  # Package name (same as AuthName directive)
     my $r    = shift;  # Apache request object
     my @cred = @_;     # Credentials from login form
     ...blah blah blah, create a session key...
     return $session_key;
 }
```
The only limitation on the session key is that you should be able to look at it later and determine the user's username. You are responsible for implementing your own session key format. A typical format is to make a string that contains the username, an expiration time, whatever else you need, and an MD5 hash of all that data together with a secret key. The hash will ensure that the user doesn't tamper with the session key.
authen_ses_key()
You must define this method yourself in your subclass of "Apache2_4::AuthCookie". Its job is to look at a session key and determine whether it is valid. If so, it returns the username of the authenticated user.
```
 sub authen_ses_key ($$$) {
     my ($self, $r, $session_key) = @_;
     ...blah blah blah, check whether $session_key is valid...
     return $ok ? $username : undef;
 }
```
Optionally, return an array of 2 or more items that will be passed to method custom_errors. It is the responsibility of this method to return the correct response to the main Apache module.
custom_errors($r,@_)
This method handles the server response when you wish to access the Apache custom_response method. Any suitable response can be used. this is particularly useful when implementing 'by directory' access control using the user authentication information. i.e.
```
        /restricted
                /one            user is allowed access here
                /two            not here
                /three          AND here
```
The authen_ses_key method would return a normal response when the user attempts to access 'one' or 'three' but return (NOT_FOUND, 'File not found') if an attempt was made to access subdirectory 'two'. Or, in the case of expired credentials, (AUTH_REQUIRED,'Your session has timed out, you must login again').
```
  example 'custom_errors'
  sub custom_errors {
      my ($self,$r,$CODE,$msg) = @_;
      # return custom message else use the server's standard message
      $r->custom_response($CODE, $msg) if $msg;
      return($CODE);
  }
  where CODE is a valid code from Apache2::Const
```
login()
This method handles the submission of the login form. It will call the "authen_cred()" method, passing it $r and all the submitted data with names like "credential_#", where # is a number. These will be passed in a simple array, so the prototype is "$self->authen_cred($r, @credentials)". After calling "authen_cred()", we set the user's cookie and redirect to the URL contained in the "destination" submitted form field.
login_form($r)
This method is responsible for displaying the login form. The default implementation will make an internal redirect and display the URL you specified with the "PerlSetVar WhatEverLoginScript" configuration directive. You can overwrite this method to provide your own mechanism.
login_form_status($r)
This method returns the HTTP status code that will be returned with the login form response. The default behaviour is to return HTTP_FORBIDDEN, except for some known browsers which ignore HTML content for HTTP_FORBIDDEN responses (e.g.: SymbianOS). You can override this method to return custom codes.
Note that HTTP_FORBIDDEN is the most correct code to return as the given request was not authorized to view the requested page. You should only change this if HTTP_FORBIDDEN does not work.
logout()
This is simply a convenience method that unsets the session key for you. You can call it in your logout scripts. Usually this looks like "$r->auth_type->logout($r);".
send_cookie($r, $session_key)
By default this method simply sends out the session key you give it. If you need to change the default behavior (perhaps to update a timestamp in the key) you can override this method.
recognize_user()
If the user has provided a valid session key but the document isn't protected, this method will set "$r->user" anyway. Use it as a PerlFixupHandler, unless you have a better idea.
key($r)
This method will return the current session key, if any. This can be handy inside a method that implements a "require" directive check (like the "species" method discussed above) if you put any extra information like clearances or whatever into the session key.
untaint_destination($self, $uri)
This method returns a modified version of the destination parameter before embedding it into the response header. Per default it escapes CR, LF and TAB characters of the uri to avoid certain types of security attacks. You can override it to more limit the allowed destinations, e.g., only allow relative uris, only special hosts or only limited set of characters.

EXAMPLE

For an example of how to use "Apache2_4::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. You might generate the page using a ModPerl::Registry script, a HTML::Mason component, an Apache handler, or perhaps even using a static HTML page. It's usually useful to generate it dynamically so that you can define the 'destination' field correctly (see below).

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 handled by the "->login()" method - see example in the SYNOPSIS section).
2.: The various user input fields (username, passwords, etc.) must be named 'credential_0', 'credential_1', etc. on the form. These will get passed to your "authen_cred()" method.
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/.

In addition, you might want your login page to be able to tell why the user is being asked to log in. In other words, if the user sent bad credentials, then it might be useful to display an error message saying that the given username or password are invalid. Also, it might be useful to determine the difference between a user that sent an invalid auth cookie, and a user that sent no auth cookie at all. To cope with these situations, AuthCookie will set "$r->subprocess_env('AuthCookieReason')" to one of the following values.

no_cookie: The user presented no cookie at all. Typically this means the user is trying to log in for the first time.
bad_cookie: The cookie the user presented is invalid. Typically this means that the user is not allowed access to the given page.
bad_credentials: The user tried to log in, but the credentials that were passed are invalid.

You can examine this value in your login form by examining "$r->prev->subprocess_env('AuthCookieReason')" (because it's a sub-request).

Of course, if you want to give more specific information about why access failed when a cookie is present, your "authen_ses_key()" method can set arbitrary entries in "$r->subprocess_env".

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/htdocs/docs/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. This usually looks like "$r->auth_type->logout($r);".

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 = Digest::SHA::sha256_hex(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 a database to store the session key and retrieve it later.

FREQUENTLY ASKED QUESTIONS

I upgraded to Apache 2.4 and now AuthCookie doesn't work!
Apache 2.4 radically changed the authenciation and authorization API. You will need to port your AuthCookie subclass over to the Apache 2.4 API. See the POD documenation in README.apache-2.4 for more information, but the quick rundown is you need to:
Inherit from "Apache2_4::AuthCookie"
Remove all "PerlAuthzHandler" configuration entries.
Write Authz Provider methods for any "Requires" directives that you are using that apache does not provide for already (e.g. apache already handles "user" and "valid-user") and register them with something like.

PerlAddAuthzProvier species Sample::AuthCookieHandler->authz_species
Replace instances of "${AuthName}Satistfy" with either "RequireAll" or "RequireAny" blocks.
Why is my authz method called twice per request?
This is normal behaviour under Apache 2.4. This is to accommodate for authorization of anonymous access. You are expected to return "Apache2::Const::AUTHZ_DENIED_NO_USER" IF "$r->user" has not yet been set if you want authentication to proceed. Your authz handler will be called a second time after the user has been authenticated.
AuthCookie authenticates, but the authorization handler is returning "UNAUTHORIZED" instead of "FORBIDDEN"!
In Apache 2.4, in "mod_authz_core", if no authz handlers return "AUTHZ_GRANTED", then "HTTP_UNAUTHORIZED" is returned. In previous versions of Apache, "HTTP_FORBIDDEN" was returned. You can get the old behaviour if you want it with:
```
 AuthzSendForbiddenOnFailure On
```
My log shows an entry like:
```
 authorization result of Require ...: denied (no authenticated user yet)
```
These are normal. This happens because the authz provider returned "AUTHZ_DENIED_NO_USER" and the authz provider will be called again after authentication happens.

HISTORY

Originally written by Eric Bartley <[email protected]>

versions 2.x were written by Ken Williams <[email protected]>

COPYRIGHT

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

SOURCE

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

BUGS

Please report any bugs or feature requests to [email protected] or through the web interface at:
http://rt.cpan.org/Public/Dist/Display.html?Name=Apache-AuthCookie

AUTHOR

Michael Schout <[email protected]>

COPYRIGHT AND LICENSE

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