I have followed this step to setup my server to enable CORS.
https://learn.microsoft.com/en-us/aspnet/web-api/overview/security/enabling-cross-origin-requests-in-web-api
But now in my browser dev console, I see this error message:
XMLHttpRequest cannot load https://serveraddress/abc. Response for
preflight is invalid (redirect)
Do you know what can I do to fix it? I am making a CORS request in HTTPS. I think that is causing the 'preflight is invalid (redirect)' failure. But I don't know why or what is redirecting the OPTIONS request.
Thank you.
Short answer: Ensure the request URL in your code isn’t missing a trailing slash.
A missing-trailing-slash problem is the most-common cause of the error cited in the question.
But that’s not the only cause — just the most common. Read on for more details.
When you see this error, it means your code is triggering your browser to send a CORS preflight OPTIONS request, and the server’s responding with a 3xx redirect. To avoid the error, your request needs to get a 2xx success response instead.
You may be able to adjust your code to avoid triggering browsers to send the OPTIONS request.
As far as what all’s going on in this case, it’s important to know browsers do a CORS preflight if:
the request method is anything other than GET, HEAD, or POST
you’ve set custom request headers other than Accept, Accept-Language, Content-Language, Content-Type, DPR, Downlink, Save-Data, Viewport-Width, or Width
the Content-Type request header has a value other than application/x-www-form-urlencoded, multipart/form-data, or text/plain
If you can’t change your code to avoid need for browsers to do a preflight, another option is:
Check the URL in the Location response header in the response to the OPTIONS request.
Change your code to make the request to that other URL directly instead.
The difference between the URLs might be something as simple as a trailing slash in the path — for example, you may need to change the URL in your code to add a trailing slash — e.g., http://localhost/api/auth/login/ (notice the trailing slash) rather than http://localhost/api/auth/login (no trailing slash) — or you might instead need to remove a trailing slash.
You can use the Network pane in browser devtools to examine the response to the OPTIONS request and to find the redirect URL in the value of the Location response header.
However, in some cases, all of the following will be true:
you’re not able to avoid the preflight OPTIONS
you’re not able to make any adjustments to the request URL
you’re not able to replace the request URL with a completely different URL
A common case with those conditions is when you try to work with some 3rd-party endpoint that requires an OAuth or SSO workflow that’s not intended to be used from frontend code.
In such cases — in all cases, actually — what’s essential to realize is that the response to the preflight must come from the same origin to which your frontend code sent the request.
So even if you create a server-side proxy that you control:
If your browser sends a preflight OPTIONS request to your proxy.
You’ve configured the proxy such that it just redirects the request to a 3rd-party endpoint.
Thus, your frontend ends up receiving a response directly from that 3rd-party endpoint.
…then the preflight will fail.
In such a case ultimately your only alternative is: ensure the preflight isn’t just redirected to the 3rd-party endpoint but instead your own server-side (proxy) code receives the response from that endpoint, consumes it, and then sends a response of its own back to your frontend code.
This happens sometimes when you try calling an https service as http, for example when you perform a request on:
'http://example.com/api/v2/tickets'
Which should be:
'https://example.com/api/v2/tickets'
First of all, ensure that you have "Access-Control-Allow-Origin": "*" in the headers
then just remove "/" at the end of url
e.g. change
url: "https://facebook/api/login/"
into
url: "https://facebook/api/login" (without '/')
In my case I did not have to set the request header to have "Access-Control-Allow-Origin": "*". The url HAD TO be ending with a "/" at the end
in my case i also solve this preflight request by just putting one slash (/) at the end of the api
#django #reactJs
The CORS request was responded to by the server with an HTTP redirect to a URL on a different origin than the original request, which is not permitted during CORS requests.
For example, if the page https://service.tld/fetchdata were requested, and the HTTP response is "301 Moved Permanently", "307 Temporary Redirect", or "308 Permanent Redirect" with a Location of https://anotherservice.net/getdata, the CORS request will fail in this manner.
To fix the problem, update your code to use the new URL as reported by the redirect, thereby avoiding the redirect.The CORS request was responded to by the server with an HTTP redirect to a URL on a different origin than the original request, which is not permitted during CORS requests.
For example, if the page https://service.tld/fetchdata were requested, and the HTTP response is "301 Moved Permanently", "307 Temporary Redirect", or "308 Permanent Redirect" with a Location of https://anotherservice.net/getdata, the CORS request will fail in this manner.
To fix the problem, update your code to use the new URL as reported by the redirect, thereby avoiding the redirect.
I'm having troubles with setting up mangopay on my react App. I'm getting this error when i try to fetch all cards of a specific user :
Access to fetch at 'https://api.sandbox.mangopay.com/v2.01/oauth/token' from origin {URL} has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
POST https://api.sandbox.mangopay.com/v2.01/oauth/token net::ERR_FAILED
I'm trying to do to it as so:
const listAvailableCard = () => {
const cards = mangopay.Users.getCards(resp.UserId);
return cards;
}
Does anyone know how to solve this issue. Considering that i already tried on both SSL certificated serve and not.
Thank you.
Vincent
The error you're seeing is a security error, however, it's not related to your request being http/s. Its known as a CORS (Cross-Origin Resource Sharing) error and has to do with blocking requests that go across origins. i.e one website calling on another website for resources.
So if you make your request in the browser from vincent.com to api.mangopay.com the request will be blocked because vincent.com isn't an origin that Mangopay trusts.
To avoid this error the best option is to make the requests to Mangopay from a server and then query your server from your client for the results.
You can read more about CORS and the related errors at these links:
https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors
Forgive me for the obvious error I am obviously committing...
I understand CORS, how and why it's used. But I'm missing the blindingly obvious in this instance.
I'm trying to access a publicly available API that should work fine (I've been assured)
If I hit the endpoint in Chrome, or in Postman, all works fine: wonderful JSON is returned.
When I try to do the same using axios from within my create-react-app's componentDidMount, I get a CORS error, specifically
Access to XMLHttpRequest at 'http://some-interesting-url/sub-url?blabla=blip&foo=bar' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
What is it I'm failing to grasp? Is there anything I can do from my end? (I have no control over the server)
The Postman app is not a browser so it isn't bound by the rules of CORS. In a browser too, trying to access a URL directly doesn't trigger Cross-Origin-Request-Sharing policies. CORS, by definition will only affects the 'cross-origin' requests made from background JS code of a web-page, to another web-page or API not hosted on same domain name.
Based on the error posted, the API in question is not sending Access-Control-Allow-Origin header. If it's possible to get the API changed, that you should get the header added to response (with value '*', or your domain name). However if that's not possible, then you'd need to route the request through a web-server that you own and include this header there. This kind of does work like a proxy, albeit for a specialized use-case.
If you already have some server side application running, you can simply add another end point to your application. A call to this new end point should trigger the 'Public API' call, and send the response back to client. Since the server side program (eg PHP/Python/NodeJS) would never be a browser, they will not face the CORS issues. If your original web-page is also loaded from same web-server, then the response header can be skipped.
XMLHttpRequest cannot load http://hfdvcbapp01.vm.itg.corp.us.shldcorp.com:8180/cnb/cnb/report/summary?Company=IT. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://127.0.0.1:64033' is therefore not allowed access.
I am getting this error when i am trying to load data from json which situated at the server.How can i resolve this.
Access-Control-Allow-Origin header should be set in the response,
if it is not from the same origin of the URL it was sent from, the header should be set from the respone - meaning - the server responding to the request in youre case - http://hfdvcbapp01.vm.itg.corp.us.shldcorp.com:8180,
if the server is under youre control just handle it, if its an outside service you should request this.
Your api is not returning header
Access-Control-Allow-Origin: http://yourdomain.com
to allow specific domain
or
Access-Control-Allow-Origin: *
to allow all
PS. Also make sure that headers are actually there. Pay attention that CORS actually send 2 requests 1 will be OPTIONS, second will be actual request so if you return headers only on GET or POST it wont work. To check it in chrome presss f12, go to network and do you requests make sure that header is there
Read more
this is a similar question to this post in SO.But the answer provided here cannot be applied in my case as i cannot change the response headers from server.
Suppose an http POST to a different origin. This implies CORS, including a CORS preflight exchange. Now suppose the OPTIONS request returns a 503 service unavailable error due to a server problem. In this case the error handler gives ""for data and 0 for status instead of giving me the status code 503 and the text:service not available. An example of this scenario is illustrated in the below image.
I am using angularjs $http and i know in the response there are no CORS header if such errors happen.and i cannot change it.
Is there any way i can receive the proper error code and the text in my rejection object.
This is not an issue of AngularJS / $http but it is the behavior of the browsers and their XMLHttpRequest object: If the CORS request fails, the browser does not give any information back to the caller.
Before I got this understanding, I also though it to be an AngularJS issue and I raised an open issue on github of Angular -> with the corresponding comment.
https://github.com/angular/angular.js/issues/13085#issuecomment-148047721
So I think there seems no other way to solve this as to add the Access-Control-Allow-Origin response header also on the proxy / load balancer in case of 503.
Edit:
If your load balancer is a HAproxy, the following may help you too:
HAproxy: different 503 errorfile for OPTIONS and POST methods
It shows how to let HAproxy anwer the CORS requests autonomous.