Instead of making a request from the client to the external API directly, you can make a request to the proxy server. Solution 2: Use a Proxy ServerĪs the same-origin policy is implemented by internet browsers and not enforced within server-to-server communication, you can use a proxy server to call the external API.Ī proxy server acts as a middleware between the client and the server. If you are using an external API service and cannot configure the backend to accept CORS requests, you can try one of the methods below.
PREFLIGHT MISSING ALLOW ORIGIN HEADER AXIOS HOW TO
This W3C Wiki shows you how to add the headers to popular servers like Apache, nginx, Jetty, etc. However, you need to be careful when using this as it could cause your server to be vulnerable to CSRF attacks.ĭifferent backend frameworks need to be configured differently to add the CORS headers. If you want to allow multiple origins, you can do it dynamically by reading the Origin header from the request and set it as the value for Access-Control-Allow-Origin.Īnother option would be to set the header to Access-Control-Allow-Origin: * to allow requests from any URL. This will allow to make a cross-origin request to your server. You can configure the backend to return this in the response header: The basic requirement is to add Access-Control-Allow-Origin to the response header to specify the origin that is allowed to access resources from the server. If you have access to the backend service, you can configure the backend to handle CORS requests if they are allowed. How to Fix a CORS Error Solution 1: Configure the Backend to Allow CORS As is not included in the Access-Control-Allow-Origin header of the response, the browser will display a CORS error. The server will return a response with some of these CORS headers to allow or block the request:Ī CORS error occurs when the server doesn’t return the CORS headers required.įor example, tries to make an API request to that doesn’t allow it to access its resources. Whenever a website tries to make a cross-origin request, the browser will add these CORS headers to the request: It relies on a mechanism that checks whether the server will permit requests from other origins to make sure that the cross-origin requests are safe.
Why Does a CORS Error OccurĬORS supports requests and data transfers between cross-origin browsers and servers to be carried out securely. To access data from other origins or post data to them, CORS is needed. Other resources such as images and CSS are not restricted and can be accessed from other origins. The same-origin policy only restricts on-page scripts from accessing data or posting data to a different origin. Without this policy, a malicious website would be able to read your sensitive information on another website by making an HTTP request to the website. The same-origin policy is a security measure to prevent Cross-Site Request Forgery (CSRF). This means that a website is only allowed to make requests to the same origin unless the response from other origins includes the right CORS headers (the CORS headers will be listed in the next section of this article). Internet browsers follow the same-origin policy and restrict cross-origin HTTP requests initiated from scripts. Two URLs would be considered to be having different origins when they have different protocols, ports (if specified), or hosts.įor example, making a request from to is considered cross-origin as they have different hostnames. It is a mechanism for relaxing the same-origin policy of modern internet browsers. The name explains itself, Cross-Origin Resource Sharing (CORS)is an HTTP mechanism that allows resource sharing from one origin to another origin securely. Method not supported under Access-Control-Allow-Methods headerīefore finding solutions to fix the error, we need to understand what is CORS.No ‘Access-Control-Allow-Headers’ headers present.No ‘Access-Control-Allow-Origin’ header present.Usually, you will see an error message Access to XMLHttpRequest has been blocked by CORS policy on the browser console followed by a cause like one of these below:
If you haven’t, you might encounter the error at some point in your development journey. There are around 13,600 questions about a CORS error asked on Stackoverflow 🥲: If you are a web developer, I believe you have encountered a CORS error before during development when working with an API.
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