# NAME

Plack::Middleware::CSRFBlock - Block CSRF Attacks with minimal changes to your app

# VERSION

version 0.06

# SYNOPSIS

    use Plack::Builder;

    my $app = sub { ... }

    builder {
      enable 'Session';
      enable 'CSRFBlock';
      $app;
    }

# DESCRIPTION

This middleware blocks CSRF. You can use this middleware without any modifications
to your application, in most cases. Here is the strategy:

- output filter

When the application response content-type is "text/html" or
"application/xhtml+xml", this inserts hidden input tag that contains token
string into `form`s in the response body.  It can also adds an optional meta
tag (by setting `add_meta` to true) with the default name "csrftoken".
For example, the application response body is:

    <html>
      <head>
          <title>input form</title>
      </head>
      <body>
        <form action="/api" method="post">
          <input type="text" name="email" /><input type="submit" />
        </form>
    </html>

this becomes:

    <html>
      <head><meta name="csrftoken" content="0f15ba869f1c0d77"/>
          <title>input form</title>
      </head>
      <body>
        <form action="/api" method="post"><input type="hidden" name="SEC" value="0f15ba869f1c0d77" />
          <input type="text" name="email" /><input type="submit" />
        </form>
    </html>

This affects `form` tags with `method="post"`, case insensitive.

- input check

For every POST requests, this module checks the `X-CSRF-Token` header first,
then `POST` input parameters. If the correct token is not found in either,
then a 403 Forbidden is returned by default.

Supports `application/x-www-form-urlencoded` and `multipart/form-data` for
input parameters, but any `POST` will be validated with the `X-CSRF-Token`
header.  Thus, every `POST` will have to have either the header, or the
appropriate form parameters in the body.

- javascript

This module can be used easily with javascript by having your javascript
provide the `X-CSRF-Token` with any ajax `POST` requests it makes.  You can
get the `token` in javascript by getting the value of the `csrftoken` `meta`
tag in the page <head>.  Here is sample code that will work for `jQuery`:

    $(document).ajaxSend(function(e, xhr, options) {
        var token = $("meta[name='csrftoken']").attr("content");
        xhr.setRequestHeader("X-CSRF-Token", token);
    });

This will include the X-CSRF-Token header with any `AJAX` requests made from
your javascript.

# OPTIONS

    use Plack::Builder;

    my $app = sub { ... }

    builder {
      enable 'Session';
      enable 'CSRFBlock',
        parameter_name => 'csrf_secret',
        token_length => 20,
        session_key => 'csrf_token',
        blocked => sub {
          [302, [Location => 'http://www.google.com'], ['']];
        },
        onetime => 0,
        ;
      $app;
    }

- parameter\_name (default:"SEC")

Name of the input tag for the token.

- meta\_tag (default:undef)

Name of the `meta` tag added to the `head` tag of
output pages.  The content of this `meta` tag will be
the token value.  The purpose of this tag is to give
javascript access to the token if needed for AJAX requests.
If this attribute is not explicitly set the meta tag will not
be included.

- header\_name (default:"X-CSRF-Token")

Name of the HTTP Header that the token can be sent in.
This is useful for sending the header for Javascript AJAX requests,
and this header is required for any post request that is not
of type `application/x-www-form-urlencoded` or `multipart/form-data`.

- token\_length (default:16);

Length of the token string. Max value is 40.

- session\_key (default:"csrfblock.token")

This middleware uses [Plack::Middleware::Session](http://search.cpan.org/perldoc?Plack::Middleware::Session) for token storage. this is
the session key for that.

- blocked (default:403 response)

The application called when CSRF is detected.

Note: This application can read posted data, but DO NOT use them!

- onetime (default:FALSE)

If this is true, this middleware uses __onetime__ token, that is, whenever
client sent collect token and this middleware detect that, token string is
regenerated.

This makes your applications more secure, but in many cases, is too strict.

# SEE ALSO

[Plack::Middleware::Session](http://search.cpan.org/perldoc?Plack::Middleware::Session)

# AUTHORS

- Rintaro Ishizaki <rintaro@cpan.org>
- William Wolf <throughnothing@gmail.com>
- Matthew Phillips <mattp@cpan.org>

# COPYRIGHT AND LICENSE

This software is copyright (c) 2012 by the Authors of Plack-Middleware-CSRFBlock.

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