HTTPS Request : CORS error but I still get data

Question

I'm making HTTPS request to a private API (hosted Itop), I get an response but I get CORS Multiple Origin Not Allow error so my JavaScript program can't use the response content.
I'm supposed to have CORS authorization

The requests are POST, made with fetch, there isn't preflight (OPTIONS) request made before (fetch did them alone for my other GET API request but didn't here)

Also some server response time is long for firefox (~2s) but it don't seems to change anything

Answer 1

It's not allowed to send multiple Access-Control-Allow-Origin headers or multiple origins in one header in the same response. In the comments, you described two same Access-Control-Allow-Origin headers in one response. Even two same origins aren't allowed. Remove one header in the backend code.

Answer 2

firefox is the best browser to identify this issue, you can fix this issue by following this path. when you sending a request from frontend,and then response will come from backend. but browser is not allowed to aceess to javascript. this is the cors error.

1.open ur backend, then create a package call CorsFilter. 2. and then create a filter servlet 3. paste this code

CorsFilter

    @WebFilter(filterName = "CorsFilter", urlPatterns = "/*")
public class CorsFilter extends HttpFilter {
    @Override
    protected void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain  chain) throws IOException, ServletException {
        String origin = req.getHeader("Origin");
        if (origin != null && origin.toLowerCase().contains(getServletContext().getInitParameter("origin"))) {
            res.setHeader("Access-Control-Allow-Origin", origin);
            res.setHeader("Access-Control-Allow-Headers", "Content-Type");
            res.setHeader("Access-Control-Expose-Headers", "Content-Type");
            if (req.getMethod().equals("OPTIONS")) {
                res.setHeader("Access-Control-Allow-Methods", "OPTIONS, GET, PUT, POST, DELETE, HEAD");
            }
        }
        chain.doFilter(req, res);
    }
}