This question really applies to any non-200 and non-redirects.
For a standard HTML site, the body of a 401 response is generally HTML, letting the client know in a pretty way that they need to login. In the case of Java, at least, you can provide a message when you throw a 401, and that msg is displayed in the client.
What (if any) is the standard way of sending that message down to the client in the case of a web service? Is the contents of the body application specific? Is there a standard header where that information could live, in which case the body would be empty?
Thanks,
Roy
All information needed to authenticate should be in the WWW-Authenticate response header field.
Related
I've run into a few problems with setting cookies, and based on the reading I've done, this should work, so I'm probably missing something important.
This situation:
Previously I received responses from my API and used JavaScript to save them as cookies, but then I found that using the set-cookie response header is more secure in a lot of situations.
I have 2 cookies: "nuser" (contains a username) and key (contains a session key). nuser shouldn't be httpOnly so that JavaScript can access it. Key should be httpOnly to prevent rogue scripts from stealing a user's session. Also, any request from the client to my API should contain the cookies.
The log-in request
Here's my current implementation: I make a request to my login api at localhost:8080/login/login (keep in mind that the web-client is hosted on localhost:80, but based on what I've read, port numbers shouldn't matter for cookies)
First the web-browser will make an OPTIONS request to confirm that all the headers are allowed. I've made sure that the server response includes access-control-allow-credentials to alert the browser that it's okay to store cookies.
Once it's received the OPTIONS request, the browser makes the actual POST request to the login API. It sends back the set-cookie header and everything looks good at this point.
The Problems
This set-up yields 2 problems. Firstly, though the nuser cookie is not httpOnly, I don't seem to be able to access it via JavaScript. I'm able to see nuser in my browser's cookie option menu, but document.cookie yeilds "".
Secondly, the browser seems to only place the Cookie request header in requests to the exact same API (the login API):
But, if I do a request to a different API that's still on my localhost server, the cookie header isn't present:
Oh, and this returns a 406 just because my server is currently configured to do that if the user isn't validated. I know that this should probably be 403, but the thing to focus on in this image is the fact that the "cookie" header isn't included among the request headers.
So, I've explained my implementation based on my current understanding of cookies, but I'm obviously missing something. Posting exactly what the request and response headers should look like for each task would be greatly appreciated. Thanks.
Okay, still not exactly what was causing the problem with this specific case, but I updated my localhost:80 server to accept api requests, then do a subsequent request to localhost:8080 to get the proper information. Because the set-cookie header is being set by localhost:80 (the client's origin), everything worked fine. From my reading before, I thought that ports didn't matter, but apparently they do.
I've been looking on the web regarding CORS, and I wanted to confirm if whatever I made of it is, what it actually is.
Mentioned below is a totally fictional scenario.
I'll take an example of a normal website. Say my html page has a form that takes a text field name. On submitting it, it sends the form data to myPage.php. Now, what happens internally is that, the server sends the request to www.mydomain.com/mydirectory/myPage.php along with the text fields. Now, the server sees that the request was fired off from the same domain/port/protocol
(Question 1. How does server know about all these details. Where does it extract all these details froms?)
Nonetheless, since the request is originated from same domain, it server the php script and returns whatever is required off it.
Now, for the sake of argument, let's say I don't want to manually fill the data in text field, but instead I want to do it programmatically. What I do is, I create a html page with javascript and fire off a POST request along with the parameters (i.e. values of textField). Now since my request is not from any domain as such, the server disregards the service to my request. and I get cross domain error?
Similarly, I could have written a Java program also, that makes use of HTTPClient/Post request and do the same thing.
Question 2 : Is this what the problem is?
Now, what CORS provide us is, that the server will say that 'anyone can access myPage.php'.
From enable cors.org it says that
For simple CORS requests, the server only needs to add the following header to its response:
Access-Control-Allow-Origin: *
Now, what exactly is the client going to do with this header. As in, the client anyway wanted to make call to the resources on server right? It should be upto server to just configure itself with whether it wants to accept or not, and act accordingly.
Question 3 : What's the use of sending a header back to client (who has already made a request to the server)?
And finally, what I don't get is that, say I am building some RESTful services for my android app. Now, say I have one POST service www.mydomain.com/rest/services/myPost. I've got my Tomcat server hosting these services on my local machine.
In my android app, I just call this service, and get the result back (if any). Where exactly did I use CORS in this case. Does this fall under a different category of server calls? If yes, then how exactly.
Furthermore, I checked Enable Cors for Tomcat and it says that I can add a filter in my web.xml of my dynamic web project, and then it will start accepting it.
Question 4 : Is that what is enabling the calls from my android device to my webservices?
Thanks
First of all, the cross domain check is performed by the browser, not the server. When the JavaScript makes an XmlHttpRequest to a server other than its origin, if the browser supports CORS it will initialize a CORS process. Or else, the request will result in an error (unless user has deliberately reduced browser security)
When the server encounters Origin HTTP header, server will decide if it is in the list of allowed domains. If it is not in the list, the request will fail (i.e. server will send an error response).
For number 3 and 4, I think you should ask separate questions. Otherwise this question will become too broad. And I think it will quickly get close if you do not remove it.
For an explanation of CORS, please see this answer from programmers: https://softwareengineering.stackexchange.com/a/253043/139479
NOTE: CORS is more of a convention. It does not guarantee security. You can write a malicious browser that disregards the same domain policy. And it will execute JavaScript fetched from any site. You can also create HTTP headers with arbitrary Origin headers, and get information from any third party server that implements CORS. CORS only works if you trust your browser.
For question 3, you need to understand the relationship between the two sites and the client's browser. As Krumia alluded to in their answer, it's more of a convention between the three participants in the request.
I recently posted an article which goes into a bit more detail about how CORS handshakes are designed to work.
Well I am not a security expert but I hope, I can answer this question in one line.
If CORS is enabled then server will just ask browser if you are calling the request from [xyz.com]? If browser say yes it will show the result and if browser says no it is from [abc.com] it will throw error.
So CORS is dependent on browser. And that's why browsers send a preflight request before actual request.
In my case I just added
.authorizeRequests().antMatchers(HttpMethod.OPTIONS, "/**").permitAll()
to my WebSecurityConfiguration file issue is resolved
We are trying to build a REST interface that allows users to test the existence of a specific resource. Let's assume we're selling domain names: the user needs to determine if the domain is available.
An HTTP GET combined with 200 and 404 response codes seems sensible at first glance.
The problem we have is discriminating between a request successfully served by our lookup service, and a request served under exceptional behaviour from other components. For example:
404 and 200 can be returned by intermediary proxies that actually block the request. This can be due to proxy misconfiguration, or even external infrastructure such as coffee shop Wifi using poor forms-based authentication.
Clients could be using broken URLs. This could occur through deprecation or (again) by misconfiguration. We could combat the former through 301, however.
What is the current best practice for discriminating between responses that have been successfully fulfilled against the client's intention for that request, and responses served through exceptional behaviour?
The problem is eliminated by tunnelling responses through the response body, as we can ensure these are unique to our service. However, doesn't seem very RESTful!
Simply have your application add some content to its HTTP responses that will distinguish them from the responses thrown by intermediaries. Any or all of these would work:
Information about the error in the response content that is recognizable as your application's content (for example, Application error: Domain name not found (404))
A Content-Type header in the response that indicates that the response content should be decoded as an application error (for example, Content-Type: application/vnd.domain-finder.error+json)
A custom header in the response that indicates it is an application error
Once you implement a scheme like this, your API clients will need to be aware of the mechanism you choose if they want to react differently to application errors versus infrastructure errors, so just document it clearly.
I tend to follow the "do what's RESTful as long as it makes sense" line of thinking.
Let's say you have an API that looks like this:
/api/v1/domains/<name>/
Hitting /api/v1/domain/exists.com/ could then return a 200 with some whois information.
Hitting /api/v1/domain/doesnt.com/ could return a 404 with links to purchase options.
That would probably work. If the returned content follows a strict format (e.g. a JSON response with a results key) then your API's responses can be differentiated from your proxies' responses.
Alternatively, you could offer
/api/v1/domains/?search=maybe
/api/v1/domains/?lookup=maybe.com
This is now slightly less RESTful but it's still self-describing and (in my opinion) not that bad. Now every response can be a 200 and your content can reveal the results.
As JSONP requests are created in the following way:
var script=document.createElement('script');
script.src='url';
script.onLoad=function(){dosomething()};
document.body.appendChild(script);
My question is that, is there a w3c standard, cross-browser supported event like onBeforeLoad which in turn let us stop executing downloaded script, in case it is not a well-formed JSONP response, or it is not passing through some predefined scheme validation, or just in case it consists of some harmful code(basic script validation)?
I know of the onBeforeLoad event supported in some browser out there, but focusing on the downloaded script datasource and in any of the reasons stated above,
it would be extemely useful to have cross-browser access to the loading script source, and due to good reasons,
the possibility to stop the execution, just before it is started.
For example the above script could be the following:
var script=document.createElement('script');
script.src='url';
script.onBeforeLoad=function(){
if(json.parseJson(this.dataSource) &&
json.validateAgainst(schema,this.dataSource))
{
return false;
}
else{
return true;
}
};
//if onBeforeLoad return true, onLoad will not be fired;
script.onLoad=function(){dosomething()};
document.body.appendChild(script);
I know that JSONP is all about trust in the 3rd party javascript module, hence i sometime wish that if i could validate those modules just before i am using it.
If you want to detect whether the JSONP response is more than the JSONP you are expecting, then no, this is not possible.
If you would be able to read the response, you wouldn’t need JSONP in the first place. Because the main reason to use JSONP is to circumvent the restrictions on accessing the response of XHR requests or via DOM due to the Same-Origin Policy. And the extension of XHR (formerly known as XHR Level 2) that allows cross-origin requests by supporting the CORS specification may not be applicable due to missing support by browsers and/or by servers.
That’s the main security concern with JSONP: You need to trust the server.
I'm stuck in a cookie related question. I want to write a program that can automate download the attachments of this forum. So I should maintain the cookies this site send to me. When I send a GET request in my program to the login page, I got the cookie such as Set-Cookie: sso_sid=0589a967; domain=.it168.com in my program. Now if I use a cookie viewer such as cookie monster and send the same GET request, my program get the same result, but the cookie viewer shows that the site also send me two cookies which are:
testcookie http://get2know.it/myimages/2009-12-27_072438.jpg and token http://get2know.it/myimages/2009-12-27_072442.jpg
My question is: Where did the two cookie came from? Why they did not show in my program?
Thanks.
Your best bet to figure out screen-scraping problems like this one is to use Fiddler. Using Fiddler, you can compare exactly what is going over the wire in your app vs. when accessing the site from a browser. I suspect you'll see some difference between headers sent by your app vs. headers sent by the browser-- this will likley account for the difference you're seeing.
Next, you can do one of two things:
change your app to send exactly the headers that the browser does (and, if you do this, you should get exactly the response that a real browser gets).
using Fiddler's "request builder" feature, start removing headers one by one and re-issuing the request. At some point, you'll remove a header which makes the response not match the response you're looking for. That means that header is required. Continue for all other headers until you have a list of headers that are required by the site to yield the response you want.
Personally, I like option #2 since it requires a minimum amount of header-setting code, although it's harder initially to figure out which headers the site requires.
On your actual question of why you're seeing 2 cookies, only the diagnosis above will tell you for sure, but I suspect it may have to do with the mechanism that some sites use to detect clients who don't accept cookies. On the first request in a session, many sites will "probe" a client to see if the client accepts cookies. Typically they'll do this:
if the request doesn't have a cookie on it, the site will redirect the client to a special "cookie setting" URL.
The redirect response, in addition to having a Location: header which does the redirect, will also return a Set-Cookie header to set the cookie. The redirect will typically contain the original URL as a query string parameter.
The server-side handler for the "cookie setter" page will then look at the incoming cookie. If it's blank, this means that the user's browser is set to not accept cookies, and the site will typically redirect the user to a "sorry, you must use cookies to use this site" page.
If, however, there is a cookie header send to the "cookie setter" URL, then the client does in fact accept cookies, and the handler will simply redirect the client back to the original URL.
The original URL, once you move on to the next page, may add an additional cookie (e.g. for a login token).
Anyway, that's one way you could end up with two cookies. Only diagnosis with Fiddler (or a similar tool) will tell you for sure, though.