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CORS policy blocks access to webapp

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Backendless Version (3.x / 5.x, Online / Managed / Pro )


Client SDK (REST / Android / Objective-C / Swift / JS )

Application ID

Expected Behavior

Please describe the expected behavior of the issue, starting from the first action.

Webapp works without CORS error in the browser console

Actual Behavior

Please provide a description of what actually happens, working from the same starting point.

Be descriptive: “it doesn’t work” does not describe what the behavior actually is – instead, say “the request returns a 400 error with message XXX”. Copy and paste your logs, and include any URLs.

After deploying the webapp a CORS error blocks requests from the browser:

Reproducible Test Case

Please provide a simple code that could be run in a new clean app and reproduce the issue.

If the issue is more complex or requires configuration, please provide a link to a project on Github that reproduces the issue.

Hello @Oliver_Donnerhak

We will investigate your problem and answer you as soon as possible.


@Oliver_Donnerhak what is the domain and port where you try to login?
also what value do you get of Access-Control-Allow-Origin header?

The following URL I try to use to login

also what value do you get of Access-Control-Allow-Origin header?

The login request does not have any header like this.
Other requests have Access-Control-Allow-Origin: *

@Oliver_Donnerhak I am toking about response Access-Control-Allow-Origin header

@sergey.kuk Yes, I know - but as the request is blocked there is no response.
You can try it at

@Oliver_Donnerhak to avoid CORS you can export request as curl

I have done it for you:

ksv@ip-192-168-1-145 ~ % curl '' -H 'Accept: application/json' -H 'Referer:' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36' -H 'Content-Type: application/json' --data-binary '{"email":"test","password":"test"}' --compressed -i

HTTP/1.1 404 Not Found
X-Powered-By: Express
Content-Security-Policy: default-src 'none'
X-Content-Type-Options: nosniff
Content-Type: text/html; charset=utf-8
Content-Length: 237
Date: Wed, 15 Apr 2020 07:37:51 GMT
Connection: keep-alive

<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<pre>Cannot POST /api/5978627C-79F8-A1C4-FFEE-82D04295B100/472ABB42-DDF0-4CDD-B324-E03E1E7DDA69/services/auth/login</pre>

As you can see your load balancer do know anything about /api/5978627C-79F8-A1C4-FFEE-82D04295B100/472ABB42-DDF0-4CDD-B324-E03E1E7DDA69/services/auth/login

and the response does not contain CORS that is why the browser does not handle the request.