# SYNOPSIS # in a lite application post '/some-url' => ( with_csrf_protection => 1 ) => sub { ... }; # in a full application $app->routes->post('/some-url') ->with_csrf_protection ->to(...); # DESCRIPTION This Mojolicious plugin provides a routing condition (called `with_csrf_protection`) and routing shortcut to add that condition (also called `with_csrf_protection`) that can be used to protect against cross site request forgery. Adding the condition to the route checks a valid CSRF token was passed, either in the `X-CSRF-Token` HTTP header or in the `crsf_token` parameter. Failing the CSRF check causes a 403 error and the `bad_csrf` template to be rendered, or if no such template is found a simple error string to be output. This behavior is unlike most conditions that can be applied to Mojolicious routes that normally just cause the route matching to fail and alternative subsequent routes to be evaluated, but immediately returning an error response makes sense for a failed CSRF check. The actual error rendering is performed by the `reply.bad_csrf` helper that this plugin installs, and if you want different error output you should override that helper. # EXAMPLES ## A Mojolicious::Lite application Here's a simple Mojolicious application that I can run on my desktop computer that creates a very simple web interface to adding things to do to my `todo.txt`. Because I don't want anyone web page on the internet to be able to tell my browser to add whatever that web page feels like to my todo list, I add CSRF protection with the `with_csrf_protection => 1` condition to the POST. #!/usr/bin/perl use Mojolicious::Lite; plugin 'WithCSRFProtection'; plugin 'TagHelpers'; get '/' => sub {} => 'index'; post '/note' => (with_csrf_protection => 1) => sub { my ($c) = @_; open my $fh, '>>', $ENV{HOME}.'/todo.txt' or die "Can't open todo: $!"; print $fh $c->param('item'), "\n"; }; app->start; __DATA__ @@ index.html.ep %= form_for note => begin %= text_field 'item' %= csrf_field %= submit_button % end @@ note.html.ep Okay, I wrote that down! The template for the index makes use of the `csrf_field` tag helper to render a hidden input field containing the current csrf\_token:
However if a bad agent causes your browser to try POSTing to the form without the CSRF token (or for that matter the corresponding session cookie), you just get the standard CSRF protection error message: shell$ curl -X POST -F 'item=transfer money to bad guys' Failed CSRF check ## A Mojolicious AJAX application In this example we have a hypothetical Mojolicious application that uses jQuery to POST some JSON to the server. To provide CSRF protection we make use of the `X-CSRF-Token` header. It's possible to configure jQuery to add additional headers on each request: Once you've done this it's further possible wherever you define your routes to require this CSRF header (or one of the `csrf_token` parameters) with the `with_csrf_protection` shortcut (which just applies the `with_csrf_protection` condition) sub startup { my ($self) = @_; $self->routes ->post('/launch-nukes') ->with_csrf_protection ->to('nuke#launch'); ... } # AUTHOR Mark Fowler # COPYRIGHT AND LICENSE This software is copyright (c) 2016 by MaxMind, Inc.. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.