[Engine-devel] Proposal to make REST API more webapp-friendly

Wed Apr 17 10:25:06 UTC 2013

Hi Oved, thanks for your feedback!

> We currently return the JSESSIONID also using HTTP headers. We currently return the jsession id also as part of the response HTTP headers, but the client still needs to pass a cookie with the appropriate value in order for the REST session to work. Isn't that enough to cope with this issue?

Right, currently REST API responds with JSESSIONID cookie + separate JSESSIONID response header, both carrying session ID value.

As I wrote in my original email: JavaScript running at [http://example.com/webapp] *cannot* get/set cookies from requests at [http://example.com/restapi]

So WebAdmin cannot get/set REST API JSESSIONID cookie directly, which is why it uses separate JSESSIONID response header in order to *read* the session ID value. As for sending JSESSIONID cookie, WebAdmin currently relies on standard cookie-handling implemented in browsers: all cookies for location X [http://example.com/restapi] will be part of any request to location X. So it's the browser who sets JSESSIONID cookie for REST API request, not WebAdmin.

To answer your question, currently it's enough to work around the cookie access limitation, but it's not good enough in my opinion (from JavaScript/webapp perspective)..

> If not, then we might be able to do option #2:
> Today, we keep the engine session ID on the HTTP session attributes.
> So, we can support either passing the cookie with the JSESSIONID (taking the engine session ID from the http session), or passing the engine session ID as HTTP header (assuming we would also return the engine session ID upon first REST request).

Well, the problem I described only relates to the way how JSESSIONID value is transmitted between client and server: currently using cookies, so REST API client has to do cookie handling.

It would be really great if I could tell REST API to use plain (i.e. *not* Set-Cookie & Cookie) HTTP header, for example "JSESSIONID", for the purpose of transmitting session ID value between client and server.

For example, the request to acquire session would be:

    GET /api HTTP/1.1
    Host: www.example.org
    Prefer: use-jsessionid-header
    JSESSIONID: xxx

[Feel free to replace "use-jsessionid-header" with anything you like. If client doesn't specify "use-jsessionid-header", server expects "Cookie" header by default to preserve compatibility.]

And the response would be:

    HTTP/1.1 200 OK
    JSESSIONID: xxx

[If client didn't specify "use-jsessionid-header", server would use "Set-Cookie" header by default to preserve compatibility.]

> This approach is problematic, as it might work well now, when the only attribute we use is the engine session ID, but in the future that might not be the case.
> If it is important enough (i.e., you can't really work with option #1) , then we can make a decision to save the attributes on the engine session, rather than on the HTTP session.
> So, we would start by supporting them both together, adding new attributes only to the engine session, and in the future deprecating the use of cookies, and only supporting HTTP headers.

I think you can keep the current implementation, i.e. use REST API HttpSession to store Engine session ID value.

The only difference would be, when REST API receives the request, it looks for "Prefer:use-jsessionid-header", and if it's present, it uses "JSESSIONID" header value to look up HttpSession in some way (not sure about implementation details, though, but this should be possible to do).

So, what do you think?

Vojtech

----- Original Message -----
From: "Oved Ourfalli" <ovedo at redhat.com>
To: "Vojtech Szocs" <vszocs at redhat.com>
Cc: "engine-devel" <engine-devel at ovirt.org>, "Juan Hernandez" <jhernand at redhat.com>, "Michael Pasternak" <mpastern at redhat.com>
Sent: Wednesday, April 17, 2013 11:13:12 AM
Subject: Re: [Engine-devel] Proposal to make REST API more webapp-friendly

----- Original Message -----
> From: "Vojtech Szocs" <vszocs at redhat.com>
> To: "engine-devel" <engine-devel at ovirt.org>
> Sent: Monday, April 15, 2013 2:04:24 PM
> Subject: [Engine-devel] Proposal to make REST API more webapp-friendly
> 
> Hi guys,
> 
> having worked with Engine REST API from web application (JavaScript)
> perspective, there are things that could be improved to make REST API more
> webapp-friendly.
> 
> First of all, webapps are *not* traditional HTTP clients, i.e. they have
> *not* full control over HTTP processing. There are some standard conventions
> and behaviors built into web browsers that any REST API implementation
> should be aware of.
> 
> --
> 
> (1) Don't force clients to use cookies for transmitting authentication
> information! (or don't use cookies at all)
> 
> Good explanation can be found at
> [http://www.berenddeboer.net/rest/cookies.html]. Cookies have many
> disadvantages:
> 
> * cookie parsing/formatting is not trivial
>   --> extra complexity imposed on REST clients
> 
> * in addition to Same-Origin Policy
> [http://en.wikipedia.org/wiki/Same_origin_policy], cookies can be get/set
> *only* for the given path
>   --> JavaScript running at [http://example.com/webapp] *cannot* get/set
>   cookies from requests at [http://example.com/restapi]
> 
> * cookies are the primary source of Cross-Site Request Forgery
> [http://en.wikipedia.org/wiki/Cross-site_request_forgery] attacks
>   --> malicious websites/scripts can forge requests to REST API that will
>   include the cookie, compromising user session
> 
> Alternative: clients could be given the *option* to use regular HTTP header
> for transmitting authentication information.
> 
> For example, webapp could read such (sensitive information) header, store it
> securely via HTML5 Session Storage
> [http://en.wikipedia.org/wiki/Web_storage] and implement related HTTP
> processing on its own, e.g. pass this header for all authenticated requests
> (instead of pushing this responsibility to browser).
> 

Option #1:
We currently return the JSESSIONID also using HTTP headers. We currently return the jsession id also as part of the response HTTP headers, but the client still needs to pass a cookie with the appropriate value in order for the REST session to work. Isn't that enough to cope with this issue?

If not, then we might be able to do option #2:
Today, we keep the engine session ID on the HTTP session attributes.
So, we can support either passing the cookie with the JSESSIONID (taking the engine session ID from the http session), or passing the engine session ID as HTTP header (assuming we would also return the engine session ID upon first REST request).

This approach is problematic, as it might work well now, when the only attribute we use is the engine session ID, but in the future that might not be the case.
If it is important enough (i.e., you can't really work with option #1) , then we can make a decision to save the attributes on the engine session, rather than on the HTTP session.
So, we would start by supporting them both together, adding new attributes only to the engine session, and in the future deprecating the use of cookies, and only supporting HTTP headers.

cc-ed Juan and Michael, as they might have some input on that.

> --
> 
> (2) Straight-forward HTTP Basic Auth has some drawbacks!
> 
> HTTP Basic Auth [http://en.wikipedia.org/wiki/Basic_access_authentication]
> over (non-secure) HTTP connection means sending user credentials
> (username/password/domain) in easy-to-decode cleartext, i.e. the value is
> *not* encrypted or hashed in any way. Using secure lower-level protocol
> (SSL) fixes the consequence, rather than the root cause of the
> confidentiality issue.
> 
> Furthermore, browsers typically remember HTTP Basic Auth information (either
> via browser-specific popup, or via XmlHttpRequest) until the browser window
> is closed. This means the webapp has no control over HTTP Basic Auth header
> after it has been set! This is the reason why it's hard to implement
> "logout" functionality in webapps when using HTTP Basic Auth.
> 
> Last but not least, HTTP Basic Auth is vulnerable to Replay attacks
> [http://en.wikipedia.org/wiki/Replay_attack]. Someone between client and
> server can intercept requests and replay them, compromising user session.
> 
> Alternative: clients could be given the *option* to use more advanced
> authentication scheme.
> 
> I've just read an excellent article at
> [http://www.thebuzzmedia.com/designing-a-secure-rest-api-without-oauth-authentication/]
> which describes easy yet secure authentication scheme inspired by Amazon Web
> Services REST API authentication
> [http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAuthentication.html].
> The idea is simple: collect auth information, hash (sign) it with a private
> key, and send everything to server. To guard against Replay attacks, just
> provide some timestamp to enforce request expiry after some time (say, 5-15
> minutes). Easy and simple!
> 
> --
> 
> (3) Support JSON for resource representations!
> 
> I think this is pretty much obvious. XML has no real advantages over JSON.
> JSON, on the other hand, has good support in webapps (JavaScript) and maps
> directly to common data structures (i.e. string, number, boolean, and so
> on).
> 
> From webapp perspective, it's much easier and natural to use JSON than to
> parse/format XML documents.
> 
> Alternative: clients could be given the *option* to use JSON, in addition to
> XML representation.
> 
> --
> 
> Vojtech
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