NextJs CORS issue

Question

I have a Next.js app hosted on Vercel at www.example.com, which needs to communicate with a backend .NET Core Web API hosted on a different server at api.example.com. The .NET core web api has been configured to allow CORS but my Next.js keeps complaining that data cannot be displayed when I use AXIOS to fetch data because the response lacks allow-cors headers:

Access to XMLHttpRequest at 'https://api.example.com' from origin 'http://www.example.com' 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

It works fine when I run it locally using npm run dev, but doesn't work when I build it and then run npm run start

Does anyone know how to fix the cors issue in production?

Answer 1

I found a solution here:

Basically, I just need to add a next.config.js file in the root directory and add the following:

// next.config.js
module.exports = {
    async rewrites() {
        return [
          {
            source: '/api/:path*',
            destination: 'https://api.example.com/:path*',
          },
        ]
      },
  };

Answer 2

I had a similar issue, I was making the call from this page:

pages/page1.js

  export default async function page1() {
       const data = await axios.post('https://www.dominio.com/xxx' , {param: 1}, headers)
}

But the solution is to make axios calls to a local API file inside "pages/api" directory, and this local API file, will handle the request to the external webserver. This avoid the CORS issue.

pages/page1.js

export default async function page1() {
        const data = await axios.post('/api/get_page1_data', {param: 1} )
}

pages/api/get_page1_data.js

export default async function handler(req, res) {
try{
   const data = await axios.post('https://www.dominio.com/xxx' , {param: req.body.param}, headers)
    res.status(200).json(data)
 } catch (error) {
    console.error(error)
    return res.status(error.status || 500).end(error.message)
  }

Answer 3

if you want to use the cors library in nextjs, I created a library for it is nextjs-cors.

https://www.npmjs.com/nextjs-cors

https://github.com/yonycalsin/nextjs-cors

pages/api/whoami.{ts,js}

import NextCors from 'nextjs-cors';

async function handler(req, res) {
   // Run the cors middleware
   // nextjs-cors uses the cors package, so we invite you to check the documentation https://github.com/expressjs/cors
   await NextCors(req, res, {
      // Options
      methods: ['GET', 'HEAD', 'PUT', 'PATCH', 'POST', 'DELETE'],
      origin: '*',
      optionsSuccessStatus: 200, // some legacy browsers (IE11, various SmartTVs) choke on 204
   });

   // Rest of the API logic
   res.json({ message: 'Hello NextJs Cors!' });
}

Answer 4

it was a problem in the server not accepting OPTIONS requests, because routes were declared as GET::sometnig or POST:: something, so the preflight couldn't pass and the POST request was decliend, hope this will help another people to prevent hours of googling, so in my case (Node.js + Express.js) i had to add this to my server.js

  app.use((req, res, next) => {
    res.header("Access-Control-Allow-Origin", "*");
    res.header(
      "Access-Control-Allow-Headers",
      "Origin, X-Requested-With, Content-Type, Accept, Authorization"
    );
  if (req.method == "OPTIONS") {
    res.header("Access-Control-Allow-Methods", "PUT, POST, PATCH, DELETE, GET");
    return res.status(200).json({});
  }

  next();
});

Answer 5

Please make sure it is CORS and is not something else. For example, in my case I was getting a 400 response. Please look on the Response tab of that request for information.

Answer 6

Do an extra check if your base URL is correct that was my issue

Answer 7

I have Next.js application that has graphql and Apollo Client setup (apollo version : 3.5.10). In order to make a query inside any component you have to use "client" variable that Apollo Client provide. You need to have apollo-client.js file in your project root so that Apollo Client can use it inside any component for query. Inside any component when you trying to make a query like: client.query(...), with these settings of apollo-client file it will throw "cors" error. However you can fix this by adding headers property inside apollo-client file.

This is OLD Settings:

apollo-client.js (old)

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'http://localhost:4000/graphql',
  cache: new InMemoryCache(),
});

export default client;

This is NEW Settings:

apollo-client.js (new)

import { ApolloClient, InMemoryCache } from '@apollo/client';

const client = new ApolloClient({
  uri: 'http://localhost:4000/graphql',
  cache: new InMemoryCache(),
  headers: {
    fetchOptions: {
      mode: 'no-cors',
    },
  },
});

export default client;

By doing this, you won't get any "cors" error while doing query inside any component.