Apparently, I have completely misunderstood its semantics. I thought of something like this:
A client downloads JavaScript code MyCode.js from http://siteA - the origin.
The response header of MyCode.js contains Access-Control-Allow-Origin: http://siteB, which I thought meant that MyCode.js was allowed to make cross-origin references to the site B.
The client triggers some functionality of MyCode.js, which in turn make requests to http://siteB, which should be fine, despite being cross-origin requests.
Well, I am wrong. It does not work like this at all. So, I have read Cross-origin resource sharing and attempted to read Cross-Origin Resource Sharing in w3c recommendation.
One thing is sure - I still do not understand how I am supposed to use this header.
I have full control of both site A and site B. How do I enable the JavaScript code downloaded from the site A to access resources on the site B using this header?
P.S.: I do not want to utilize JSONP.
Access-Control-Allow-Origin is a CORS (cross-origin resource sharing) header.
When Site A tries to fetch content from Site B, Site B can send an Access-Control-Allow-Origin response header to tell the browser that the content of this page is accessible to certain origins. (An origin is a domain, plus a scheme and port number.) By default, Site B's pages are not accessible to any other origin; using the Access-Control-Allow-Origin header opens a door for cross-origin access by specific requesting origins.
For each resource/page that Site B wants to make accessible to Site A, Site B should serve its pages with the response header:
Access-Control-Allow-Origin: http://siteA.com
Modern browsers will not block cross-domain requests outright. If Site A requests a page from Site B, the browser will actually fetch the requested page on the network level and check if the response headers list Site A as a permitted requester domain. If Site B has not indicated that Site A is allowed to access this page, the browser will trigger the XMLHttpRequest's error event and deny the response data to the requesting JavaScript code.
Non-simple requests
What happens on the network level can be slightly more complex than explained above. If the request is a "non-simple" request, the browser first sends a data-less "preflight" OPTIONS request, to verify that the server will accept the request. A request is non-simple when either (or both):
using an HTTP verb other than GET or POST (e.g. PUT, DELETE)
using non-simple request headers; the only simple requests headers are:
Accept
Accept-Language
Content-Language
Content-Type (this is only simple when its value is application/x-www-form-urlencoded, multipart/form-data, or text/plain)
If the server responds to the OPTIONS preflight with appropriate response headers (Access-Control-Allow-Headers for non-simple headers, Access-Control-Allow-Methods for non-simple verbs) that match the non-simple verb and/or non-simple headers, then the browser sends the actual request.
Supposing that Site A wants to send a PUT request for /somePage, with a non-simple Content-Type value of application/json, the browser would first send a preflight request:
OPTIONS /somePage HTTP/1.1
Origin: http://siteA.com
Access-Control-Request-Method: PUT
Access-Control-Request-Headers: Content-Type
Note that Access-Control-Request-Method and Access-Control-Request-Headers are added by the browser automatically; you do not need to add them. This OPTIONS preflight gets the successful response headers:
Access-Control-Allow-Origin: http://siteA.com
Access-Control-Allow-Methods: GET, POST, PUT
Access-Control-Allow-Headers: Content-Type
When sending the actual request (after preflight is done), the behavior is identical to how a simple request is handled. In other words, a non-simple request whose preflight is successful is treated the same as a simple request (i.e., the server must still send Access-Control-Allow-Origin again for the actual response).
The browsers sends the actual request:
PUT /somePage HTTP/1.1
Origin: http://siteA.com
Content-Type: application/json
{ "myRequestContent": "JSON is so great" }
And the server sends back an Access-Control-Allow-Origin, just as it would for a simple request:
Access-Control-Allow-Origin: http://siteA.com
See Understanding XMLHttpRequest over CORS for a little more information about non-simple requests.
Cross-Origin Resource Sharing - CORS (A.K.A. Cross-Domain AJAX request) is an issue that most web developers might encounter, according to Same-Origin-Policy, browsers restrict client JavaScript in a security sandbox, usually JS cannot directly communicate with a remote server from a different domain. In the past developers created many tricky ways to achieve Cross-Domain resource request, most commonly using ways are:
Use Flash/Silverlight or server side as a "proxy" to communicate
with remote.
JSON With Padding (JSONP).
Embeds remote server in an iframe and communicate through fragment or window.name, refer here.
Those tricky ways have more or less some issues, for example JSONP might result in security hole if developers simply "eval" it, and #3 above, although it works, both domains should build strict contract between each other, it neither flexible nor elegant IMHO:)
W3C had introduced Cross-Origin Resource Sharing (CORS) as a standard solution to provide a safe, flexible and a recommended standard way to solve this issue.
The Mechanism
From a high level we can simply deem CORS as a contract between client AJAX call from domain A and a page hosted on domain B, a typical Cross-Origin request/response would be:
DomainA AJAX request headers
Host DomainB.com
User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0
Accept text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8,application/json
Accept-Language en-us;
Accept-Encoding gzip, deflate
Keep-Alive 115
Origin http://DomainA.com
DomainB response headers
Cache-Control private
Content-Type application/json; charset=utf-8
Access-Control-Allow-Origin DomainA.com
Content-Length 87
Proxy-Connection Keep-Alive
Connection Keep-Alive
The blue parts I marked above were the kernal facts, "Origin" request header "indicates where the cross-origin request or preflight request originates from", the "Access-Control-Allow-Origin" response header indicates this page allows remote request from DomainA (if the value is * indicate allows remote requests from any domain).
As I mentioned above, W3 recommended browser to implement a "preflight request" before submiting the actually Cross-Origin HTTP request, in a nutshell it is an HTTP OPTIONS request:
OPTIONS DomainB.com/foo.aspx HTTP/1.1
If foo.aspx supports OPTIONS HTTP verb, it might return response like below:
HTTP/1.1 200 OK
Date: Wed, 01 Mar 2011 15:38:19 GMT
Access-Control-Allow-Origin: http://DomainA.com
Access-Control-Allow-Methods: POST, GET, OPTIONS, HEAD
Access-Control-Allow-Headers: X-Requested-With
Access-Control-Max-Age: 1728000
Connection: Keep-Alive
Content-Type: application/json
Only if the response contains "Access-Control-Allow-Origin" AND its value is "*" or contain the domain who submitted the CORS request, by satisfying this mandtory condition browser will submit the actual Cross-Domain request, and cache the result in "Preflight-Result-Cache".
I blogged about CORS three years ago: AJAX Cross-Origin HTTP request
According to this Mozilla Developer Network article,
A resource makes a cross-origin HTTP request when it requests a resource from a different domain, or port than the one which the first resource itself serves.
An HTML page served from http://domain-a.com makes an <img> src request for http://domain-b.com/image.jpg.
Many pages on the web today load resources like CSS style sheets, images and scripts from separate domains (thus it should be cool).
Same-Origin Policy
For security reasons, browsers restrict cross-origin HTTP requests initiated from within scripts.
For example, XMLHttpRequest and Fetch follow the same-origin policy.
So, a web application using XMLHttpRequest or Fetch could only make HTTP requests to its own domain.
Cross-Origin Resource Sharing (CORS)
To improve web applications, developers asked browser vendors to allow cross-domain requests.
The Cross-origin resource sharing (CORS) mechanism gives web servers cross-domain access controls, which enable secure cross-domain data transfers.
Modern browsers use CORS in an API container - such as XMLHttpRequest or fetch - to mitigate risks of cross-origin HTTP requests.
How CORS works (Access-Control-Allow-Origin header)
Wikipedia:
The CORS standard describes new HTTP headers which provide browsers and servers a way to request remote URLs only when they have permission.
Although some validation and authorization can be performed by the server, it is generally the browser's responsibility to support these headers and honor the restrictions they impose.
Example
The browser sends the OPTIONS request with an Origin HTTP header.
The value of this header is the domain that served the parent page. When a page from http://www.example.com attempts to access a user's data in service.example.com, the following request header would be sent to service.example.com:
Origin: http://www.example.com
The server at service.example.com may respond with:
An Access-Control-Allow-Origin (ACAO) header in its response indicating which origin sites are allowed.
For example:
Access-Control-Allow-Origin: http://www.example.com
An error page if the server does not allow the cross-origin request
An Access-Control-Allow-Origin (ACAO) header with a wildcard that allows all domains:
Access-Control-Allow-Origin: *
Whenever I start thinking about CORS, my intuition about which site hosts the headers is incorrect, just as you described in your question. For me, it helps to think about the purpose of the same-origin policy.
The purpose of the same-origin policy is to protect you from malicious JavaScript on siteA.com accessing private information you've chosen to share only with siteB.com. Without the same-origin policy, JavaScript written by the authors of siteA.com could have your browser make requests to siteB.com, using your authentication cookies for siteB.com. In this way, siteA.com could steal the secret information you share with siteB.com.
Sometimes you need to work cross domain, which is where CORS comes in. CORS relaxes the same-origin policy for siteB.com, using the Access-Control-Allow-Origin header to list other domains (siteA.com) that are trusted to run JavaScript that can interact with siteB.com.
To understand which domain should serve the CORS headers, consider this. You visit malicious.com, which contains some JavaScript that tries to make a cross domain request to mybank.com. It should be up to mybank.com, not malicious.com, to decide whether or not it sets CORS headers that relax the same-origin policy, allowing the JavaScript from malicious.com to interact with it. If malicous.com could set its own CORS headers allowing its own JavaScript access to mybank.com, this would completely nullify the same-origin policy.
I think the reason for my bad intuition is the point of view I have when developing a site. It's my site, with all my JavaScript. Therefore, it isn't doing anything malicious, and it should be up to me to specify which other sites my JavaScript can interact with. When in fact I should be thinking: Which other sites' JavaScript are trying to interact with my site and should I use CORS to allow them?
From my own experience, it's hard to find a simple explanation why CORS is even a concern.
Once you understand why it's there, the headers and discussion becomes a lot clearer. I'll give it a shot in a few lines.
It's all about cookies. Cookies are stored on a client by their domain.
An example story: On your computer, there's a cookie for yourbank.com. Maybe your session is in there.
Key point: When a client makes a request to the server, it will send the cookies stored under the domain for that request.
You're logged in on your browser to yourbank.com. You request to see all your accounts, and cookies are sent for yourbank.com. yourbank.com receives the pile of cookies and sends back its response (your accounts).
If another client makes a cross origin request to a server, those cookies are sent along, just as before. Ruh roh.
You browse to malicious.com. Malicious makes a bunch of requests to different banks, including yourbank.com.
Since the cookies are validated as expected, the server will authorize the response.
Those cookies get gathered up and sent along - and now, malicious.com has a response from yourbank.
Yikes.
So now, a few questions and answers become apparent:
"Why don't we just block the browser from doing that?" Yep. That's CORS.
"How do we get around it?" Have the server tell the request that CORS is OK.
1. A client downloads javascript code MyCode.js from http://siteA - the origin.
The code that does the downloading - your html script tag or xhr from javascript or whatever - came from, let's say, http://siteZ. And, when the browser requests MyCode.js, it sends an Origin: header saying "Origin: http://siteZ", because it can see that you're requesting to siteA and siteZ != siteA. (You cannot stop or interfere with this.)
2. The response header of MyCode.js contains Access-Control-Allow-Origin: http://siteB, which I thought meant that MyCode.js was allowed to make cross-origin references to the site B.
no. It means, Only siteB is allowed to do this request. So your request for MyCode.js from siteZ gets an error instead, and the browser typically gives you nothing. But if you make your server return A-C-A-O: siteZ instead, you'll get MyCode.js . Or if it sends '*', that'll work, that'll let everybody in. Or if the server always sends the string from the Origin: header... but... for security, if you're afraid of hackers, your server should only allow origins on a shortlist, that are allowed to make those requests.
Then, MyCode.js comes from siteA. When it makes requests to siteB, they are all cross-origin, the browser sends Origin: siteA, and siteB has to take the siteA, recognize it's on the short list of allowed requesters, and send back A-C-A-O: siteA. Only then will the browser let your script get the result of those requests.
Using React and Axios, join a proxy link to the URL and add a header as shown below:
https://cors-anywhere.herokuapp.com/ + Your API URL
Just adding the proxy link will work, but it can also throw an error for No Access again. Hence it is better to add a header as shown below.
axios.get(`https://cors-anywhere.herokuapp.com/[YOUR_API_URL]`,{headers: {'Access-Control-Allow-Origin': '*'}})
.then(response => console.log(response:data);
}
Warning: Not to be used in production
This is just a quick fix. If you're struggling with why you're not able to get a response, you can use this.
But again it's not the best answer for production.
If you are using PHP, try adding the following code at the beginning of the php file:
If you are using localhost, try this:
header("Access-Control-Allow-Origin: *");
If you are using external domains such as server, try this:
header("Access-Control-Allow-Origin: http://www.website.com");
I worked with Express.js 4, Node.js 7.4 and Angular, and I had the same problem. This helped me:
a) server side: in file app.js I add headers to all responses, like:
app.use(function(req, res, next) {
res.header('Access-Control-Allow-Origin', req.headers.origin);
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
next();
});
This must be before all routes.
I saw a lot of added this headers:
res.header("Access-Control-Allow-Headers","*");
res.header('Access-Control-Allow-Credentials', true);
res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
But I don’t need that,
b) client side: in sending by Ajax, you need to add "withCredentials: true," like:
$http({
method: 'POST',
url: 'url',
withCredentials: true,
data : {}
}).then(function(response){
// Code
}, function (response) {
// Code
});
If you want just to test a cross-domain application in which the browser blocks your request, then you can just open your browser in unsafe mode and test your application without changing your code and without making your code unsafe.
From macOS, you can do this from the terminal line:
open -a Google\ Chrome --args --disable-web-security --user-data-dir
In Python, I have been using the Flask-CORS library with great success. It makes dealing with CORS super easy and painless. I added some code from the library's documentation below.
Installing:
pip install -U flask-cors
Simple example that allows CORS for all domains on all routes:
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app)
#app.route("/")
def helloWorld():
return "Hello, cross-origin-world!"
For more specific examples, see the documentation. I have used the simple example above to get around the CORS issue in an Ionic application I am building that has to access a separate flask server.
Simply paste the following code in your web.config file.
Noted that, you have to paste the following code under <system.webServer> tag
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
<add name="Access-Control-Allow-Headers" value="Content-Type" />
<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
</customHeaders>
</httpProtocol>
I can't configure it on the back-end server, but with these extensions in the browsers, it works for me:
For Firefox:
CORS Everywhere
For Google Chrome:
Allow CORS: Access-Control-Allow-Origin
Note: CORS works for me with this configuration:
For cross origin sharing, set header: 'Access-Control-Allow-Origin':'*';
Php: header('Access-Control-Allow-Origin':'*');
Node: app.use('Access-Control-Allow-Origin':'*');
This will allow to share content for different domain.
Nginx and Apache
As an addition to apsiller's answer, I would like to add a wiki graph which shows when a request is simple or not (and OPTIONS pre-flight request is send or not)
For a simple request (e.g., hotlinking images), you don't need to change your server configuration files, but you can add headers in the application (hosted on the server, e.g., in PHP) like Melvin Guerrero mentions in his answer - but remember: if you add full CORS headers in your server (configuration) and at same time you allow simple CORS in the application (e.g., PHP), this will not work at all.
And here are configurations for two popular servers:
turn on CORS on Nginx (nginx.conf file)
location ~ ^/index\.php(/|$) {
...
add_header 'Access-Control-Allow-Origin' "$http_origin" always; # if you change "$http_origin" to "*" you shoud get same result - allow all domain to CORS (but better change it to your particular domain)
add_header 'Access-Control-Allow-Credentials' 'true' always;
if ($request_method = OPTIONS) {
add_header 'Access-Control-Allow-Origin' "$http_origin"; # DO NOT remove THIS LINES (doubled with outside 'if' above)
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Max-Age' 1728000; # cache preflight value for 20 days
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS'; # arbitrary methods
add_header 'Access-Control-Allow-Headers' 'My-First-Header,My-Second-Header,Authorization,Content-Type,Accept,Origin'; # arbitrary headers
add_header 'Content-Length' 0;
add_header 'Content-Type' 'text/plain charset=UTF-8';
return 204;
}
}
turn on CORS on Apache (.htaccess file)
# ------------------------------------------------------------------------------
# | Cross-domain Ajax requests |
# ------------------------------------------------------------------------------
# Enable cross-origin Ajax requests.
# http://code.google.com/p/html5security/wiki/CrossOriginRequestSecurity
# http://enable-cors.org/
# change * (allow any domain) below to your domain
Header set Access-Control-Allow-Origin "*"
Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS, DELETE, PUT"
Header always set Access-Control-Allow-Headers "My-First-Header,My-Second-Header,Authorization, content-type, csrf-token"
Header always set Access-Control-Allow-Credentials "true"
The Access-Control-Allow-Origin response header indicates whether the
response can be shared with requesting code from the given origin.
Header type Response header
-------------------------------------------
Forbidden header name no
A response that tells the browser to allow code from any origin to
access a resource will include the following:
Access-Control-Allow-Origin: *
For more information, visit Access-Control-Allow-Origin...
For .NET Core 3.1 API With Angular
Startup.cs : Add CORS
//SERVICES
public void ConfigureServices(IServiceCollection services){
//CORS (Cross Origin Resource Sharing)
//=====================================
services.AddCors();
}
//MIDDLEWARES
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseRouting();
//ORDER: CORS -> Authentication -> Authorization)
//CORS (Cross Origin Resource Sharing)
//=====================================
app.UseCors(x=>x.AllowAnyHeader().AllowAnyMethod().WithOrigins("http://localhost:4200"));
app.UseHttpsRedirection();
}
}
Controller : Enable CORS For Authorized Controller
//Authorize all methods inside this controller
[Authorize]
[EnableCors()]
public class UsersController : ControllerBase
{
//ActionMethods
}
Note: Only a temporary solution for testing
For those who can't control the backend for Options 405 Method Not Allowed, here is a workaround for theChrome browser.
Execute in the command line:
"C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" --disable-web-security --user-data-dir="path_to_profile"
Example:
"C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" --disable-web-security --user-data-dir="C:\Users\vital\AppData\Local\Google\Chrome\User Data\Profile 2"
Most CORS issues are because you are trying to request via client side ajax from a react, angular, jquery apps that are frontend basic libs.
You must request from a backend application.
You are trying to request from a frontend API, but the API you are trying to consume is expecting this request to be made from a backend application and it will never accept client side requests.
So, I have my localhost with a page, which sends request to a remote site. I try to do it like so:
Ext.Ajax.cors = true;
Ext.Ajax.request({
url: "http://remoteaddress.com",
method: "GET",
headers: {
"Access-Control-Allow-Origin": "*"
},
cors: true,
useDefaultXhrHeader: false,
success: function (result, request) {
console.log("success!!!");
}
});
So, I followed dozens of threads and set these parameters - cors, useDefaultXhrHeader etc, but to no avail.
However, if I build the same request in postman (request to the same remoteaddress.com), then it's ok.
So, what I'm doing wrong and how can I fix it?
The request with the OPTIONS-method is a preflight request.
From msdna:
A CORS preflight request is a CORS request that checks to see if the
CORS protocol is understood.
It is an OPTIONS request, using three HTTP request headers:
Access-Control-Request-Method, Access-Control-Request-Headers, and the
Origin header.
A preflight request is automatically issued by a browser, when needed.
In normal cases, front-end developers don't need to craft such
requests themselves.
The webserver has to answer it with the headers to allow the browser to do the actual request.
HTTP/1.1 200 OK
Content-Length: 0
Connection: keep-alive
Access-Control-Allow-Origin: localhost
Access-Control-Allow-Methods: POST, GET, OPTIONS, DELETE
Access-Control-Max-Age: 86400
Here is a quick fix for that
Open terminal and run this code
open -n -a /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --args --user-data-dir="/tmp/chrome_dev_sess_1" --disable-web-security
Then just use that new chrome window for development and once you host your website somewhere it will not cause an issue anymore
*note this is MacOs chrome *
I'm implementing CORS with credentials and a preflight request and I'm a bit mystified why the preflight request consistently fails in Firefox 30 but works in Safari (7.0.2) and Chrome 35. I think this issue is different from "Why does the preflight OPTIONS request of an authenticated CORS request work in Chrome but not Firefox?" because I am not getting a 401, but rather a CORS-specific message from the browser client:
"Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://myurl.dev.com. This can be fixed by moving the resource to the same domain or enabling CORS."
Without showing source code, here's what I'm doing:
On the server:
Headers for OPTIONS response:
Access-Control-Allow-Origin: [[copy origin from the request here]]
Access-Control-Allow-Methods: "POST GET OPTIONS"
Access-Control-Allow-Headers: "X-Requested-With"
Access-Control-Allow-Credentials: "true"
Headers for POST response:
Access-Control-Allow-Origin: [[copy origin from the request here]]
Access-Control-Allow-Credentials: "true"
In the browser client:
jQuery.ajax({
url: requestUrl,
type: 'POST',
data: getData(),
xhrFields: {
withCredentials: true
}
});
Per the spec, this will trigger a OPTIONS preflight request which needs to have the CORS headers in its response. I've read through the W3C spec several times and I can't identify what I'm doing wrong, if anything, in that preflight response.
QUESTION: "Why is this CORS request failing only in Firefox?"
ANSWER: While unrelated to the OP's specific case, it may help you to know that Firefox does not trust CA's (certificate authorities) in the Windows Certificate Store by default, and this can result in failing CORS requests in Firefox (as was alluded to by Svish in the question comments).
To allow Firefox to trust CA's in the Windows Certificate Store:
In Firefox, type about:config in the address bar
If prompted, accept any warnings
Right-click to create a new boolean value, and enter security.enterprise_roots.enabled as the Name
Set the value to true
Then re-test the failing request
Answer source: https://support.umbrella.com/hc/en-us/articles/115000669728-Configuring-Firefox-to-use-the-Windows-Certificate-Store
Note that Firefox is the only browser that is compliant here. If parsing of Access-Control-Allow-Methods fails per https://fetch.spec.whatwg.org/#cors-preflight-fetch a network error needs to be returned. And per the ABNF for the header value it is most definitely a comma-separated value.
Disabling HTTPS-Only Mode in Firefox solved the issue for me.
I was trying to access a remote resource using HTTP from http://localhost.
Since Firefox 87 (released in March 2021), it's possible to set the below preference in about:config, namely the Firefox Configuration Editor:
network.cors_preflight.allow_client_cert: true
From Firefox for Enterprise 87 - Release notes:
Corporations that use TLS client certificates can flip the network.cors_preflight.allow_client_cert preference to get Google Chrome-compatible handling of the CORS protocol. In particular, contrary to the Fetch Standard, this will transmit TLS client certificates along with a CORS preflight. See bug 1511151 for more information.
References:
https://support.mozilla.org/en-US/kb/firefox-enterprise-87-release-notes
https://bugzilla.mozilla.org/show_bug.cgi?id=1511151
I have noticed that when you a send CORS(Cross Origin Resource Sharing) request with cookies set, Firefox doesn't send the required response headers.
Solution:
Below solution adds headers only for OPTIONS requests and accepts requests only from example.com. You can change the implementation for other request methods and expected hosts.
JS CODE
var xmlhttp = new XMLHttpRequest();
xmlhttp.withCredentials = true;
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == XMLHttpRequest.DONE) {
if (xmlhttp.status == 200) {
success_callback(xmlhttp.responseText);
} else {
error_callback(xmlhttp.statusText);
}
}
};
xmlhttp.open("DELETE", url);
xmlhttp.send(null);
When you send a DELETE request, the browser send a pre-flight request for OPTIONS, which expects Access-Control-Allow-Methods in the response headers. Based on this header value the actual DELETE request is sent. In Firefox, when you send a DELETE request the pre-flight request's response headers do not have expected headers, therefore it fails to send the actual DELETE request.
To overcome this problem use the below NGINX server config.
NGINX CODE
#handle CORS requests by adding required headers
if ($http_origin ~* .example.com) {
set $cors "CORS-${request_method}";
}
if ($cors = "CORS-OPTIONS") {
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Allow-Headers' 'Content-Type';
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, DELETE';
add_header 'Access-Control-Allow-Origin' $http_origin;
}
Good read on CORS: https://www.html5rocks.com/en/tutorials/cors/
I am making an ajax request using $.ajax. The response has the Set-Cookie header set (I've verified this in the Chrome dev tools). However, the browser does not set the cookie after receiving the response! When I navigate to another page within my domain, the cookie is not sent. (Note: I'm not doing any cross-domain ajax requests; the request is in the same domain as the document.)
What am I missing?
EDIT: Here is the code for my ajax request:
$.post('/user/login', JSON.stringify(data));
Here is the request, as shown by the Chrome dev tools:
Request URL:https://192.168.1.154:3000/user/login
Request Method:POST
Status Code:200 OK
Request Headers:
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Content-Length:35
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
DNT:1
Host:192.168.1.154:3000
Origin:https://192.168.1.154:3000
Referer:https://192.168.1.154:3000/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36
X-Requested-With:XMLHttpRequest
Form Data:
{"UserId":"blah","Password":"blah"}:
Response:
Response Headers:
Content-Length:15
Content-Type:application/json; charset=UTF-8
Date:Sun, 16 Mar 2014 03:25:24 GMT
Set-Cookie:SessionId=MTM5NDk0MDMyNHxEdi1CQkFFQ180SUFBUkFCRUFBQVRfLUNBQUVHYzNSeWFXNW5EQXNBQ1ZObGMzTnBiMjVKWkFaemRISnBibWNNTGdBc1ZFcDNlU3RKVFdKSGIzQlNXRkkwVjJGNFJ6TlRVSHA0U0ZJd01XRktjMDF1Y1c1b2FGWXJORzV4V1QwPXwWf1tz-2Fy_Y4I6fypCzkMJyYxhgM3LjVHGAlKyrilRg==; HttpOnly
OK, so I finally figured out the problem. It turns out that setting the Path option is important when sending cookies in an AJAX request. If you set Path=/, e.g.:
Set-Cookie:SessionId=foo; Path=/; HttpOnly
...then the browser will set the cookie when you navigate to a different page. Without setting Path, the browser uses the "default" path. Apparently, the default path for a cookie set by an AJAX request is different from the default path used when you navigate to a page directly. I'm using Go/Martini, so on the server-side I do this:
session.Options(session.Options{HttpOnly: true, Path:"/"})
I'd guess that Python/Ruby/etc. have a similar mechanism for setting Path.
See also: cookies problem in PHP and AJAX
#atomkirk's answer didn't apply to me because
I don't use the fetch API
I was making cross-site requests (i.e. CORS)
NOTE: If your server is using Access-Control-Allow-Origins:* (aka "all origins"/"wildcard origins"), you may not be able to send credentials (see below).
As for the fetch API; CORS requests will need {credentials:'include'} for both sending & receiving cookies
For CORS requests, use the "include" value to allow sending
credentials to other domains:
fetch('https://example.com:1234/users', {
credentials: 'include'
})
... To opt into accepting cookies from the server, you must use the credentials option.
{credentials:'include'} just sets xhr.withCredentials=true
Check fetch code
if (request.credentials === 'include') {
xhr.withCredentials = true
}
So plain Javascript/XHR.withCredentials is the important part.
If you're using jQuery, you can set withCredentials (remember to use crossDomain: true) using $.ajaxSetup(...)
$.ajaxSetup({
crossDomain: true,
xhrFields: {
withCredentials: true
}
});
If you're using AngularJS, the $http service config arg accepts a withCredentials property:
$http({
withCredentials: true
});
If you're using Angular (Angular IO), the common.http.HttpRequest service options arg accepts a withCredentials property:
this.http.post<Hero>(this.heroesUrl, hero, {
withCredentials: true
});
As for the request, when xhr.withCredentials=true; the Cookie header is sent
Before I changed xhr.withCredentials=true
I could see Set-Cookie name & value in the response, but Chrome's "Application" tab in the Developer Tools showed me the name and an empty value
Subsequent requests did not send a Cookie request header.
After the change xhr.withCredentials=true
I could see the cookie's name and the cookie's value in the Chrome's "Application" tab (a value consistent with the Set-Cookie header).
Subsequent requests did send a Cookie request header with the same value, so my server treated me as "authenticated"
As for the response: the server may need certain Access-Control... headers
For example, I configured my server to return these headers:
Access-Control-Allow-Credentials:true
Access-Control-Allow-Origin:https://{your-origin}:{your-port}
EDIT: this approach won't work if you allow all origins/wildcard origins, as described here (thanks to #ChandanBhattad) :
The CORS request was attempted with the credentials flag set, but the server is configured using the wildcard ("*") as the value of Access-Control-Allow-Origin, which doesn't allow the use of credentials.
Until I made this server-side change to the response headers, Chrome logged errors in the console like
Failed to load https://{saml-domain}/saml-authn: Redirect from https://{saml-domain}/saml-redirect has been blocked by CORS policy:
The value of the 'Access-Control-Allow-Credentials' header in the response is '' which must be 'true' when the request's credentials mode is 'include'. Origin https://{your-domain} is therefore not allowed access.
The credentials mode of requests initiated by the XMLHttpRequest is controlled by the withCredentials attribute.
After making this Access-* header change, Chrome did not log errors; the browser let me check the authenticated responses for all subsequent requests.
If you're using the new fetch API, you can try including credentials:
fetch('/users', {
credentials: 'same-origin'
})
That's what fixed it for me.
In particular, using the polyfill: https://github.com/github/fetch#sending-cookies
This may help somebody randomly falling across this question.
I found forcing a URL with https:// rather than http:// even though the server hasn't got a certificate and Chrome complains will fix this issue.
In my case, the cookie size exceeded 4096 bytes (Google Chrome). I had a dynamic cookie payload that would increase in size.
Browsers will ignore the set-cookie response header if the cookie exceeds the browsers limit, and it will not set the cookie.
See here for cookie size limits per browser.
I know this isn't the solution, but this was my issue, and I hope it helps someone :)