Provided by: libplack-middleware-crossorigin-perl_0.009-1_all 
NAME
Plack::Middleware::CrossOrigin - Adds headers to allow Cross-Origin Resource Sharing
VERSION
version 0.009
SYNOPSIS
# Allow any WebDAV or standard HTTP request from any location.
builder {
enable 'CrossOrigin', origins => '*';
$app;
};
# Allow GET and POST requests from any location, cache results for 30 days.
builder {
enable 'CrossOrigin',
origins => '*', methods => ['GET', 'POST'], max_age => 60*60*24*30;
$app;
};
DESCRIPTION
Adds Cross Origin Request Sharing headers used by modern browsers to allow
"XMLHttpRequest" to work across domains. This module will also help protect against CSRF
attacks in some browsers.
This module attempts to fully conform to the CORS spec, while allowing additional
flexibility in the values specified for the of the headers.
CORS REQUESTS IN BRIEF
There are two types of CORS requests. Simple requests, and preflighted requests.
Simple Requests
A simple request is one that could be generated by a standard HTML form. Either a "GET"
or "POST" request, with no additional headers. For these requests, the server processes
the request as normal, and attaches the correct CORS headers in the response. The browser
then decides based on those headers whether to allow the client script access to the
response.
Preflighted Requests
If additional headers are specified, or a method other than "GET" or "POST" is used, the
request must be preflighted. This means that the browser will first send a special
request to the server to check if access is allowed. If the server allows it by
responding with the correct headers, the actual request is then performed.
CSRF Protection
Some browsers will also provide same headers with cross domain "POST" requests from HTML
forms. These requests will also be checked against the allowed origins and rejected
before they reach the rest of your Plack application.
CONFIGURATION
origins A list of allowed origins. Origins should be formatted as a URL scheme and host,
with no path information. ("http://www.example.com") '"*"' can be specified to
allow access from any location. Must be specified for this middleware to have any
effect. This will be matched against the "Origin" request header, and will
control the "Access-Control-Allow-Origin" response header. If the origin does not
match, the request is aborted.
headers A list of allowed request headers. '"*"' can be specified to allow any headers.
Controls the "Access-Control-Allow-Headers" response header. Includes a set of
headers by default to simplify working with WebDAV and AJAX frameworks:
• "Cache-Control"
• "Depth"
• "If-Modified-Since"
• "User-Agent"
• "X-File-Name"
• "X-File-Size"
• "X-Prototype-Version"
• "X-Requested-With"
methods A list of allowed methods. '*' can be specified to allow any methods. Controls
the "Access-Control-Allow-Methods" response header. Defaults to all of the
standard HTTP and WebDAV methods.
max_age The max length in seconds to cache the response data for. Controls the
"Access-Control-Max-Age" response header. If not specified, the web browser will
decide how long to use.
expose_headers
A list of allowed headers to expose to the client. '*' can be specified to allow
the browser to see all of the response headers. Controls the
"Access-Control-Expose-Headers" response header.
credentials
Whether the resource will be allowed with user credentials (cookies, HTTP
authentication, and client-side SSL certificates) supplied. Controls the
"Access-Control-Allow-Credentials" response header.
continue_on_failure
Normally, simple requests with an Origin that hasn't been allowed will be stopped
before they continue to the main app. If this option is set, the request will be
allowed to continue, but no CORS headers will be added to the response. This
matches how non-allowed requests would be handled if this module was not used at
all.
This disables the CSRF protection and is not recommended. It could be needed for
applications that need to allow cross-origin HTML form "POST"s without
whitelisting domains.
BROWSER SUPPORT
Different browsers have different levels of support for CORS headers.
Gecko (Firefox, Seamonkey)
Initially supported in Gecko 1.9.1 (Firefox 3.5). Supports the complete CORS spec
for "XMLHttpRequest"s.
Does not yet provide the "Origin" header for CSRF protection (Bugzilla #446344
<https://bugzilla.mozilla.org/show_bug.cgi?id=446344>).
WebKit (Safari, Google Chrome)
Initially supported in Safari 4 and Chrome 3. Supports the complete CORS spec.
The "expose_headers" feature has been supported since WebKit v535.18 (Safari 6,
Chrome 18). Preflighted requests were buggy prior to WebKit v534.19 (Safari 5.1,
Chrome 11), but this module uses a workaround where possible (using the "Referer"
header).
Also provides the "Origin" header for CSRF protection starting with WebKit v528.5
(Chrome 2, Safari 4).
Internet Explorer
Initially supported in IE8. Not supported with the standard "XMLHttpRequest"
object. A separate object, "XDomainRequest", must be used. Only "GET" and "POST"
methods are allowed. No extra headers can be added to the request. Neither the
status code or any headers aside from "Content-Type" can be retrieved from the
response.
IE10 supports CORS via the standard "XMLHttpRequest" object.
Opera Opera and Opera Mobile support CORS since version 12.
SEE ALSO
CORS Resources
• W3C Spec for Cross-Origin Resource Sharing <http://www.w3.org/TR/cors/>
• Mozilla Developer Center - HTTP Access Control
<https://developer.mozilla.org/En/HTTP_access_control>
• Mozilla Developer Center - Server-Side Access Control
<https://developer.mozilla.org/En/Server-Side_Access_Control>
• Cross browser examples of using CORS requests
<http://www.nczonline.net/blog/2010/05/25/cross-domain-ajax-with-cross-origin-
resource-sharing/>
• MSDN - XDomainRequest Object <http://msdn.microsoft.com/en-
us/library/cc288060%28v=vs.85%29.aspx>
• XDomainRequest - Restrictions, Limitations and Workarounds
<http://blogs.msdn.com/b/ieinternals/archive/2010/05/13/xdomainrequest-restrictions-
limitations-and-workarounds.aspx>
• Wikipedia - Cross-Origin Resource Sharing <http://en.wikipedia.org/wiki/Cross-
Origin_Resource_Sharing>
• CORS advocacy <http://enable-cors.org/>
CSRF Resources
• Wikipedia - Cross-site request forgery <http://en.wikipedia.org/wiki/Cross-
site_request_forgery>
• Stanford Web Security Research - Cross-Site Request Forgery
<http://seclab.stanford.edu/websec/csrf/>
• WebKit Bugzilla - Add origin header to POST requests
<https://bugs.webkit.org/show_bug.cgi?id=20792>
• Mozilla Bugzilla - Implement Origin header CSRF mitigation
<https://bugzilla.mozilla.org/show_bug.cgi?id=446344>
Related Technologies
• Cross-domain policy file for Flash
<http://www.adobe.com/devnet/articles/crossdomain_policy_file_spec.html>
• Wikipedia - JSONP <http://en.wikipedia.org/wiki/JSONP>
AUTHOR
Graham Knop <haarg@haarg.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2011 by Graham Knop.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.