[express] Request header field Access-Control-Allow-Headers is not allowed by itself in preflight response

I have come across CORS issues multiple times and can usually fix it but I want to really understand by seeing this from a MEAN stack paradigm.

Before I simply added middleware in my express server to catch these things, but it looks like there is some kind of pre-hook that is erroring out my requests.

Request header field Access-Control-Allow-Headers is not allowed by Access-Control-Allow-Headers in preflight response

I assumed that I could do this:

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Headers","*")
})

or the equivalent but this doesn't seem to fix it. I also of course tried

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Headers","Access-Control-Allow-Headers")
})

Still no luck.

I too faced the same problem in Angular 6. I solved the issue by using below code. Add the code in component.ts file.

import { HttpHeaders } from '@angular/common/http';

headers;

constructor() {
    this.headers = new HttpHeaders();
    this.headers.append('Access-Control-Allow-Headers', 'Authorization');
}

getData() {
    this.http.get(url,this.headers). subscribe (res => {
    // your code here...
})}

In Chrome:

Request header field X-Requested-With is not allowed by Access-Control-Allow-Headers in preflight response.

For me, this error was triggered by a trailing space in the URL of this call.

jQuery.getJSON( url, function( response, status, xhr ) {
   ...
}

const express = require('express')
const cors = require('cors')
const app = express()

app.get('/with-cors', cors(), (req, res, next) => {
  res.json({ msg: 'WHOAH with CORS it works!  ' })
})

Adding cors in get function Is what worked for me

I just ran into this issue myself, in the context of ASP.NET make sure your Web.config looks like this:

  <system.webServer>
<modules>
  <remove name="FormsAuthentication" />
</modules>

<handlers>
  <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
  <!--<remove name="OPTIONSVerbHandler"/>-->
  <remove name="TRACEVerbHandler" />
  <!--
  <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
  -->
</handlers>

<httpProtocol>
  <customHeaders>
    <add name="Access-Control-Allow-Origin" value="*" />
    <add name="Access-Control-Allow-Headers" value="Content-Type, Authorization" />
    <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
  </customHeaders>
</httpProtocol>

Notice the Authorization value for the Access-Control-Allow-Headers key. I was missing the Authorization value, this config solves my issue.

That same issue i was facing.

I did a simple change.

  <modulename>.config(function($httpProvider){
    delete $httpProvider.defaults.headers.common['X-Requested-With'];
});

res.setHeader('Access-Control-Allow-Headers', '*');

This problem solved with

 "Origin, X-Requested-With, Content-Type, Accept, Authorization"

Particular in my project (express.js/nodejs)

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, Authorization");
  next();
});

Update:

Every time error: Access-Control-Allow-Headers is not allowed by itself in preflight response error you can see what wrong with chrome developer tool:

above error is missing Content-Type so add string Content-Type to Access-Control-Allow-Headers

If you are trying to add a custom header on the request headers, you have to let the server know that specific header is allowed to take place. The place to do that is in the class that filters the requests. In the example shown below, the custom header name is "type":

public class CorsFilter implements Filter {
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        response.setHeader("Access-Control-Allow-Origin",  request.getHeader("Origin"));
        response.setHeader("Access-Control-Allow-Credentials", "true");
        response.setHeader("Access-Control-Allow-Methods", "GET,PUT,POST,DELETE,PATCH,OPTIONS");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "Content-Type, Accept, X-Requested-With, remember-me, Authorization, type ");
        response.setHeader("Access-Control-Expose-Headers","Authorization");
    }
}

Message is clear that 'Authorization' is not allowed in API. Set
Access-Control-Allow-Headers: "Content-Type, Authorization"

I received the error the OP stated using Django, React, and the django-cors-headers lib. To fix it with this stack, do the following:

In settings.py add the below per the official documentation.

from corsheaders.defaults import default_headers

CORS_ALLOW_HEADERS = default_headers + (
'YOUR_HEADER_NAME',
)

Very good i used this on a silex project

$app->after(function (Request $request, Response $response) {
        $response->headers->set('Access-Control-Allow-Origin', '*');
        $response->headers->set("Access-Control-Allow-Credentials", "true");
        $response->headers->set("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
        $response->headers->set("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, Authorization");
    });

this problem occurs when we make custom header for request.This request that uses the HTTP OPTIONS and includes several headers.

The required header for this request is Access-Control-Request-Headers , which should be part of response header and should allow request from all the origin. Sometimes it needs Content-Type as well in header of response. So your response header should be like that -

response.header("Access-Control-Allow-Origin", "*"); // allow request from all origin
response.header("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
response.header("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, Origin, X-Requested-With, Content-Type, Accept, Authorization");

To add to the other answers. I had the same problem and this is the code i used in my express server to allow REST calls:

app.all('*', function(req, res, next) {
  res.header('Access-Control-Allow-Origin', 'URLs to trust of allow');
  res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');
  res.header('Access-Control-Allow-Headers', 'Content-Type');
  if ('OPTIONS' == req.method) {
  res.sendStatus(200);
  } else {
    next();
  }
});

What this code basically does is intercepts all the requests and adds the CORS headers, then continue with my normal routes. When there is a OPTIONS request it responds only with the CORS headers.

EDIT: I was using this fix for two separate nodejs express servers on the same machine. In the end I fixed the problem with a simple proxy server.

Just to add that you can put those headers also to Webpack config file. I needed them as in my case as I was running webpack dev server.

devServer: {
    headers: {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Credentials": "true",
      "Access-Control-Allow-Methods": "GET,HEAD,OPTIONS,POST,PUT",
      "Access-Control-Allow-Headers": "Origin, X-Requested-With, Content-Type, Accept, Authorization"
    }
},

The accepted answer is ok, but I had difficulties to understand it. So here is a simple example to clarify it.

In my ajax request I had a standard Authorization header.

$$(document).on('ajaxStart', function(e){
var auth_token = localStorage.getItem(SB_TOKEN_MOBILE);
if( auth_token ) {
    var xhr = e.detail.xhr;

    xhr.setRequestHeader('**Authorization**', 'Bearer ' + auth_token);
}

This code produces the error in the question. What I had to do in my nodejs server was to add Authorization in allowed headers:

res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type,**Authorization**');

After spending almost a day, I just found out that adding the below two codes solved my issue.

Add this in the Global.asax

protected void Application_BeginRequest()
{
  if (Request.HttpMethod == "OPTIONS")
  {
    Response.StatusCode = (int)System.Net.HttpStatusCode.OK;             
    Response.End();
  }
}

and in the web config add the below

<httpProtocol>
  <customHeaders>
    <add name="Access-Control-Allow-Origin" value="*" />        
    <add name="Access-Control-Allow-Methods" value="*" />
    <add name="Access-Control-Allow-Headers" value="Content-Type, Authorization" />
  </customHeaders>
</httpProtocol>

This is what you need to add to make it work.

response.setHeader("Access-Control-Allow-Origin", "*");
response.setHeader("Access-Control-Allow-Credentials", "true");
response.setHeader("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
response.setHeader("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers");

The browser sends a preflight request (with method type OPTIONS) to check if the service hosted on the server is allowed to be accessed from the browser on a different domain. In response to the preflight request if you inject above headers the browser understands that it is ok to make further calls and i will get a valid response to my actual GET/POST call. you can constraint the domain to which access is granted by using Access-Control-Allow-Origin", "localhost, xvz.com" instead of * . ( * will grant access to all domains)

In Post API call we are sending data in request body. So if we will send data by adding any extra header to an API call. Then first OPTIONS API call will happen and then post call will happen. Therefore, you have to handle OPTION API call first.

You can handle the issue by writing a filter and inside that you have to check for option call API call and return a 200 OK status. Below is the sample code:

package com.web.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.connector.Response;

public class CustomFilter implements Filter {
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        HttpServletRequest httpRequest = (HttpServletRequest) req;
        response.setHeader("Access-Control-Allow-Origin", "*");
        response.setHeader("Access-Control-Allow-Methods", "POST, GET, PUT, OPTIONS, DELETE");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Headers", "x-requested-with, Content-Type");
        if (httpRequest.getMethod().equalsIgnoreCase("OPTIONS")) {
            response.setStatus(Response.SC_OK);
        }
        chain.doFilter(req, res);
    }

    public void init(FilterConfig filterConfig) {
        // TODO
    }

    public void destroy() {
        // Todo
    }

}