docs: more work

[cgi-auth-flexible.git] / caf.pod

# -*- fundamental -*-

=head1 NAME

CGI::Auth::Flexible - web authentication optionally using cookies

=head1 SYNOPSYS

 my $verifier = CGI::Auth::Flexible->new_verifier(setting => value,...);
 my $authreq = $verifier->new_request($cgi_query_object);

 # simple applications
 $authreq->check_ok() or return;

 # sophisticated applications
 my $divert_kind = $authreq->check_divert();
 if ($divert_kind) { ... print diversion page and quit ... }

 # while handling the request
 $user = $authreq->get_username();
 $authreq->check_mutate();

=head1 DESCRIPTION

CGI::Auth::Flexible is a library which you can use to add a
forms/cookie-based login facility to a Perl web application.

CGI::Auth::Flexible doesn't interfere with your application's URL path
namespace and just needs a few (configurable) form parameter and
cookie name(s) for its own use.  It tries to avoid making assumptions
about the implementation structure of your application.

Because CGI::Auth::Flexible is licenced under the AGPLv3, you will
probably need to provide a facility to allow users (even ones not
logged in) to download the source code for your web app.  Conveniently
by default CGI::Auth::Flexible provides (for pure Perl webapps) a
mechanism for users to get the source.

CGI::Auth::Flexible is designed to try to stop you accidentally
granting access by misunderstanding the API.  (Also it, of course,
guards against cross-site scripting.)  You do need to make sure to
call CGI::Auth::Flexible before answering AJAX requests as well as
before generating HTML pages, of course, and to call it in every
entrypoint to your system.

=head2 CHECKLIST

As a minimum you need to do all of the things on this checklist, where
applicable.  The items marked SECURITY are the ones that you might
forget: without them your application may appear to work, but will be
insecure.

=over

=item *

Call C<new_verifier> (once at application startup)

=item *

Call C<new_request> (once per request)

=item *

B<SECURITY>: Call C<check_ok> or C<check_divert> on every request, and
honour the return value.

=item *

If you're using C<check_ok>, implement either the
C<username_password_error> or C<login_ok> hook.

=item *

Call C<get_username> when you need to know who's logged in.

=item *

B<SECURITY>: Call C<check_mutate> or C<mutate_ok>, if you specified
C<promise_check_mutate>.

=item *

B<SECURITY>: Call C<check_nonpage> for every request which is not a page load
(if your application has any of those).

=item *

When generating URLs and forms (including AJAX requests), include the
hidden form parameter using C<secret_hidden_val> or
C<secret_hidden_html> when appropriate (see below).

=item *

B<SECURITY>: If you do not override the source provision facility (see
L</SOURCE CODE DOWNLOAD>), check that the assumptions it makes aren't
going to leak security-critical data.

=back

These points will now be covered in more detail.

=head2 INITIALISATION

Your application should, on startup (eg, when it is loaded by
mod_perl) do
C<< $verifier = CGI::Auth::Flexible->new_verifier(settings...) >>.
This call can be expensive and is best amortised.

The resulting verifier object can be used to process individual
requests, in each case with
C<< $authreq = CGI::Auth::Flexible->new_request($cgi_query) >>.

=head2 RESPONSES - SIMPLE APPLICATIONS

The simplist usage is to call C<< $request->check_ok() >> which will
check the user's authentication.  If the user is not logged in it will
generate a login form (or redirection or other appropriate page) and
return false; your application should not then processing that request
any further.  If the user is logged in it will return true.

Various hooks are provided to customise the responses generated by
C<check_ok>.

After C<check_ok> returns true you should go ahead and process the
request; you can use C<< $request->get_username >> to find out which
user the request came from.

=head2 RESPONSES - SOPHISTICATED APPLICATIONS

If you want to handle the control flow and to generate login forms,
redirections, etc., yourself, you can say
C<< $divert = $request->check_divert >>.  This returns undef if
the user is logged in, or I<divert spec> if some kind of login
page or diversion should be generated.

=head2 MUTATING OPERATIONS AND EXTERNAL LINKS - MUTATION-IGNORANT APPLICATIONS

By default CGI::Auth::Flexible does not permit external links into
your site.  All GET requests give a "click to continue" page which
submits a form which loads your app's main page.  In this
configuration all your application's forms and AJAX requests should
use C<POST>.  This restriction arises from complicated deficiencies
in the web's security architecture.

Such applications are also not able to provide user-specific CSS
stylesheets, javascript, favicons, etc.

=head2 MUTATING OPERATIONS AND EXTERNAL LINKS - MUTATION-AWARE APPLICATIONS

The alternative is for your application to always make a special check
when the incoming request is going to do some kind of action (such as
modifying the user's setup, purchasing goods, or whatever) rather than
just retrieve and/or display information.  We term such requests
"mutating" requests.

Then non-mutating pages can be linked to from other, untrustworthy,
websites.

To support external links, and C<GET> requests, pass
C<< promise_check_mutate => 1 >> in I<settings>, and then call
C<< $authreq->check_mutate() >> before taking any actions.  If the
incoming request is not suitable then C<< $authreq->check_mutate() >>
will call C<die>.

There have to be no mutating C<GET> requests in your application (but
you shouldn't have any of those anyway); if there are, they won't
work.  (CGI::Auth::Flexible will spot them and cause them to fail,
rather than allow them to be insecure.)

=head2 GENERATING URLS, FORMS AND AJAX QUERIES

When you generate a URL, C<POST> form or AJAX request you may need to
include a secret hidden form parameter for the benefit of
CGI::Auth::Generic.  This form parameter will be checked by
C<check_ok>/C<check_divert> and should be ignored by your application.

By default the hidden parameter is called C<caf_assochash>.

After calling C<check_ok> or C<check_divert> the value to put in your
form can be obtained from C<secret_hidden_val>; C<secret_hidden_html>
will generate the whole HTML C<< <input...> >> element.

=head3 Mutation-ignorant applications

For mutation-ignorant applications (see above), all forms etc. should
include the hidden parameter (and as discussed, they must all use
POST rather than GET).

=head3 Mutation-aware applications

For mutation-aware applications, whether to include the secret
parameter depends on the kind of request.  CGI::Auth::Flexible knows
when it is necessary.  You should find out by calling
C<need_add_hidden>.

If it is inconvenient to call C<need_add_hidden> at runtime, you can
rely instead on the following promises:  All POST requests (which
includes all mutating requests) need the parameter.  The return value
of need_add_hidden depends only on the $method and $reqtype
parameters, so you can query it once and remember the answer.
HTML page load GETs do not need the parameter.  It is better to
err on the side of including the parameter.

If you really must, you can call C<need_add_hidden> "on the bench"
during development and bake the answer into your application code
structure.  However, if you do that and a new vulnerability was
discovered which is fixed by changing the answer, updating
CGI::Auth::Flexible wouldn't be sufficient to fix it.

=head3 Mutation-aware applications - non-page requests

If your mutation-aware application supports non-page resources (AJAX
and JSON requests, stylesheets, favicons, etc.) it must inform
CGI::Auth::Flexible when it is handling such a request, by calling
C<check_nonpage>.

Normally C<check_nonpage> will simply return (and you can ignore the
return value).  However, if there is an attack (or, perhaps, a bug) it
will die, stopping the attack.

(You do not need to call C<check_nonpage> for POST requests, but it is
harmless to do so.)

=head2 DATA STORAGE

CGI::Auth::Flexible needs to store various information in plain files;
it does this in the directory specified by the C<dir> parameter.

=head1 SOURCE CODE DOWNLOAD

By default, CGI::Auth::Flexible provides a facility for users to
download the source code for the running version of your web
application.

This facility makes a number of important assumptions which you need
to check.  Note that if the provided facility is not sufficient
because your application is more sophisticated than it copes with (or
if you disable the builtin facility), you may need to implement a
functioning alternative to avoid violating the AGPLv3 licence.

Here are the most important (default) assumptions:

=over

=item *

Your app's source code is available by looking at @INC, $0 and
S<$ENV{'SCRIPT_FILENAME'}> (the B<source items>).  See
C<srcdump_listitems>.  Where these point to files or directories under
revision control, the source item is the whole containing vcs tree.

=item *

Specifically, there are no compiled or autogenerated Perl
files, Javascript resources, etc., which are not contained in one of
the source item directories.  (Files which came with your operating
system install don't need to be shipped as they fall under the system
library exception.)

=item *

You have not installed any modified versions of system
libraries (including system-supplied Perl modules) in C</usr> outside
C</usr/local>.  See C<srcdump_system_dir>.

=item *

For each source item in a dvcs, the entire dvcs history does
not contain anything confidential (or libellous).  Also, all files which
contain secrets are in the dvcs's I<.ignore> file.  See
C<srcdump_vcsscript_git> et al.

=item *

For each source item NOT in a dvcs, there are no confidential
files with the world-readable bit set (being in a world-inaccessible
directory is not sufficient).  See C<srcdump_excludes>.

=item *

You have none of your app's source code in C</etc>.

=item *

You don't regard pathnames on your server as secret.

=item *

You don't intentionally load Perl code by virtue of C<.>
being in C<@INC> by default.  (See C<srcdump_filter_cwd>.)

=back

=head1 MAIN FUNCTIONS AND METHODS

=over

=item C<< CGI::Auth::Flexible->new_verifier(setting => value, ...) >>

Initialises an instance and returns a verifier object.
The arguments are setting pairs like a hash initialiser.
See L</SETTINGS> below.

=item C<< $verifier->new_request($cgi_query) >>

Prepares to process a request.  I<$cgi_query> should normally
be the query object from L<CGI(3perl)>.  Most of the default
hook methods assume that it is; however if you replace enough of
the hook methods then you can pass any value you like and it
will be passed to your hooks.

The return value is the authentication request object (I<$authreq>)
which is used to check the incoming request and will contain
information about its credentials.

=item C<< $authreq->check_divert() >>

Checks whether the user is logged in.  Returns undef if the user is
logged in and we should service the request.  Otherwise returns a
divert spec (see L</DIVERT SPEC>) saying what should happen instead.

This method may die if it doesn't like the request, in which case
the request needs to be rejected.

=item C<< $authreq->check_ok() >>

Checks whether the user is logged in.  Returns true if the user is
logged in and we should service the request.

Otherwise it handles the request itself, generating any appropriate
redirect, login form, or continuation page.  It then returns false and
the application should not process the request further.

=item C<< $verifier->disconnect() >>

Discards the resources (open files, etc.) in the verifier object.

=back

=head REQUEST-HANDLING FUNCTIONS AND METHODS

All of these are only valid after C<check_divert> or C<check_ok> has
been called.  (In the case of C<check_ok> it won't normally be sensible
to call these functions unless C<check_ok> returned true.)

=item C<< $authreq->get_divert() >>

Returns the value previously returned by C<check_divert>.

=item C<< $authreq->get_username() >>

Returns the name of the logged-in user.  If the user was not logged
in (or their session had timed out, or something), returns undef.

=head RESPONSE-RELATED FUNCTIONS AND METHODS

=item C<< $authreq->url_with_query_params($params, [$nonpagetype]) >>

Convenience function which returns a url for a GET request to this
application.

I<$params> is a hashref specifying the parameters and the PATH_INFO.
The keys are the parameter names, and the values are array refs with
the parameter value(s) (as strings, as yet unquoted).  (They are array
refs because it is possible to pass multiple values for the same
parameter in a single request; normally each arrayref would be a
singleton.)

The request path will be the path to the application.  If a parameter
with name C<< '' >> is supplied, it is taken as the PATH_INFO to
supply - its value will be appended to the application path.  (It
should normally start with C<< / >>, and only one value should be
supplied.)

=item C<< $authreq->chain_params() >>

Returns a hash of the "relevant" parameters to this request, in a form
used by XXX.  This is all of the query parameters which are not
related to CGI::Auth::Flexible.  The PATH_INFO from the request is
returned as the parameter C<< '' >>.

=back