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Cross-domain problems are a very common problem in web development. Especially in applications with separate front-end and back-end applications, the front-end may need to access resources under different domain names, and the browser will block cross-domain requests by default for security reasons. At this time, the server needs to set HTTP headers to allow cross-domain requests. In PHP, we can use the header() function to set cross-domain related header information.
Cross-domain resource sharing (CORS) is a mechanism that solves cross-domain problems by allowing browsers to initiate requests to different domains. CORS mainly relies on HTTP headers, especially Access-Control-Allow-Origin . When a browser initiates a request to a server in a different domain, the server needs to include Access-Control-Allow-Origin in the response header to explicitly allow cross-domain requests.
Access-Control-Allow-Origin is a key header in the CORS standard, which determines which domain names can access resources. Its value can be in the following cases:
* : means that all domain names can access the resource.
http://m66.net : Only this specified domain name is allowed to access resources.
null : means that cross-domain requests are not allowed.
For example, when we want to allow the domain name http://m66.net to make cross-domain requests, we need to set the corresponding header in the PHP script.
In PHP, setting HTTP header information is implemented through the header() function. To allow cross-domain requests, the most basic step is to set Access-Control-Allow-Origin using header() .
<?php
// Allow fromhttp://m66.netCross-domain requests
header("Access-Control-Allow-Origin: http://m66.net");
// If you need to support otherHTTPmethod（likePOST、PUT、DELETEwait），This can be set：
header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE");
// like果需要允许携带cookie，You need to set the following header
header("Access-Control-Allow-Credentials: true");
// Set the allowed request header
header("Access-Control-Allow-Headers: Content-Type, Authorization");
// In practical application，You can determine the source domain name of the request，To dynamically set cross-domain headers
$allowedOrigin = "http://m66.net";
if ($_SERVER['HTTP_ORIGIN'] === $allowedOrigin) {
header("Access-Control-Allow-Origin: $allowedOrigin");
}
?>
Access-Control-Allow-Origin : Allows the specified domain name to make cross-domain requests. If you want to allow multiple domain names, you can dynamically determine the source of the request and set different domain names.
Access-Control-Allow-Methods : Allowed HTTP methods (such as GET, POST, etc.).
Access-Control-Allow-Credentials : If you need to send a cookie, you need to set the header to true .
Access-Control-Allow-Headers : Allowed custom request headers (such as Content-Type or Authorization ).
When the browser initiates some complex cross-domain requests (such as with custom headers or using PUT, DELETE methods, etc.), the browser will first send an OPTIONS request, called a preflight request. This request is to check whether the server allows cross-domain requests. In the response to the preflight request, the server also needs to return the corresponding CORS header.
For example:
<?php
if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
// Process pre-flight requests
header("Access-Control-Allow-Origin: http://m66.net");
header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE");
header("Access-Control-Allow-Headers: Content-Type, Authorization");
header("Access-Control-Allow-Credentials: true");
exit();
}
?>
OPTIONS requests do not need to return actual data, but the CORS header needs to be set correctly to tell the browser server whether cross-domain requests are allowed.
By using PHP's header() function, we can easily set cross-domain related HTTP headers, especially Access-Control-Allow-Origin , to allow cross-domain requests for specified domain names. According to actual needs, we can flexibly configure CORS policies to ensure a balance between security and functionality.
Cross-domain resource sharing is a problem that cannot be ignored in web applications. Mastering how to configure CORS headers in PHP can help you solve cross-domain problems and improve the accessibility and scalability of your application.
