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From "Jason Smith (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Wed, 31 Aug 2011 01:53:10 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13094246#comment-13094246
] 

Jason Smith commented on COUCHDB-431:
-------------------------------------

CORS is about cross-site security. Which *origins* should CouchDB trus? Which third-party
sites may query Couch through their users' browser and with their users' credentials? The
answer is clear: none of them, except by explicit permission.

Setting DB _security is not sufficient. CouchDB should be secure by default. But the latest
patch permits (forces!) authenticated queries from every origin.

Even with _security, foreign sites might access /_config, /_status, /_restart, and /_log.
Any site on the web might guess your Couch URL (localhost:5984 and well-known cloud couches
perhaps) and query it as you. If you logged in as admin (naughty!) then they can edit /_config.
If you logged in as a user, they can at least check /_all_dbs and probe for an unprotected
DB (one with the default config).

None of this should be possible, and that is why my 3-month-old patch takes the following
precautions:

1. Disabled by default
2. Simple configuration model: which origins do you trust? Put them on the whitelist.
3. Subsequent versions (whoops, not attached) disallow all cross-origin admin queries. verify_is_server_admin/1
always fails if an "Origin" header is present.

> Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
> -----------------------------------------------------------------------------------
>
>                 Key: COUCHDB-431
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-431
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>    Affects Versions: 0.9
>            Reporter: James Burke
>            Assignee: Benoit Chesneau
>            Priority: Minor
>             Fix For: 1.2
>
>         Attachments: 0001-cors-support.-should-fix-COUCHDB-431-2.patch, 0001-cors-support.-should-fix-COUCHDB-431.patch,
0001-cors-support.-should-fix-COUCHDB-431.patch, 0001-cors-support.-should-fix-COUCHDB-431.patch,
0001-cors-support.-should-fix-COUCHDB-431.patch, 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, cors_test.html, test_cors2-1.tgz,
test_cors2.tgz
>
>
> 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:
> http://dev.w3.org/2006/waf/access-control/
> 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):
> https://developer.mozilla.org/en/HTTP_access_control
> And information on Safari/Webkit (functionality in latest WebKit and Safari 4):
> http://developer.apple.com/safari/library/documentation/AppleApplications/Conceptual/SafariJSProgTopics/Articles/XHR.html
> IE 8 also uses the Access Control spec, but the requests have to go through their XDomainRequest
object (XDR):
> http://msdn.microsoft.com/en-us/library/cc288060%28VS.85%29.aspx
> 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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