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From "Jason Smith (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Tue, 17 May 2011 03:30:47 GMT


Jason Smith commented on COUCHDB-431:

Whoops, Access-Control-Request-Method and Access-Control-Request-Headers.

Anyway, the _security object would have some benefits. I already had to add another patch
to disable _admin stuff with CORS because it's just too scary. If ever got
hacked, or if somebody got untrusted javascript code hosted there, that code would have ADMIN
access to your couch.

So my new patch has _config/httpd/cors_admin = true/false (default false) so that no CORS
request can ever run with server _admin permissions.

With a _security object, there's some flexibility.

1. Indicate whether to allow CORS for the db _admin too (default would be false).
2. See the CORS policy from validate_doc_update() because it will be in secObj.

So you might have a _security:

{ "admins": { "roles": [ "my_app_admins" ] },
  "readers": {},
  "cors": { "": true // Implied anonymous access only
            "": { "timeout": 86400 }, // Also anonymous-only
            "": { "timeout": 86400, "allow_credentials": true
}, // Authenticated access
            "": { "timeout": 86400, "allow_credentials": true,
"allow_admin":true }, // Authenticated access, including db admin
However I am stopping here to get some discussion going before writing more code. I am super
excited about Couch CORS however 

> Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
> -----------------------------------------------------------------------------------
>                 Key: COUCHDB-431
>                 URL:
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>    Affects Versions: 0.9
>            Reporter: James Burke
>            Priority: Minor
>         Attachments: A_0001-Generalize-computing-the-appropriate-headers-for-any.patch,
A_0002-Send-server-headers-for-externals-responses.patch, A_0003-Usably-correct-w3c-CORS-headers-for-valid-requests.patch,
A_0004-Respond-to-CORS-preflight-checks-HTTP-OPTIONS.patch, cors.html
> Historically, browsers have been restricted to making XMLHttpRequests (XHRs) to the same
origin (domain) as the web page making the request. However, the latest browsers now support
cross-domain requests by implementing the Access Control spec from the W3C:
> In order to keep older servers safe that assume browsers only do same-domain requests,
the Access Control spec requires the server to opt-in to allow cross domain requests by the
use of special HTTP headers and supporting some "pre-flight" HTTP calls.
> Why should CouchDB support this: in larger, high traffic site, it is common to serve
the static UI files from a separate, differently scaled server complex than the data access/API
server layer. Also, there are some API services that are meant to be centrally hosted, but
allow API consumers to use the API from different domains. In these cases, the UI in the browser
would need to do cross domain requests to access CouchDB servers that act as the API/data
access server layer.
> JSONP is not enough in these cases since it is limited to GET requests, so no POSTing
or PUTing of documents.
> Some information from Firefox's perspective (functionality available as of Firefox 3.5):
> And information on Safari/Webkit (functionality in latest WebKit and Safari 4):
> IE 8 also uses the Access Control spec, but the requests have to go through their XDomainRequest
object (XDR):
> and I thought IE8 only allowed GET or POST requests through their XDR.
> But as far as CouchDB is concerned, implementing the Access Control headers should be
enough, and hopefully IE 9 will allow normal xdomain requests via XHR.

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