解决跨域 No Access-Control-Allow-Origin

在A网站中，我们希望使用Ajax来获得B网站中的特定内容。如果A网站与B网站不在同一个域中，那么就出现了跨域访问问题。你可以理解为两个域名之间不能跨过域名来发送请求或者请求数据，否则就是不安全的。跨域访问违反了同源策略，
同源策略规定，浏览器的ajax只能访问跟它的HTML页面同源（相同域名或IP）的资源。

如何确定是跨域请求
A域名资源请求到B/C……域名
你当前访问的域名是http的当请求的部分资源是https的
当使用ajax访问远程服务器时，请求失败，浏览器报如上错误。这是出于安全的考虑，默认禁止跨域访问导致的。
如果是跨域访问，这时候就会报错

has been blocked by CORS policy: No 'Access-Control-Allow-Origin'

错误场景如：我的Xiadmin报错：Fonts –No 'Access-Control-Allow-Origin' 已经提示我的请求http url跨域了，然后根据我用的服务环境设置如下就行：

直接服务器层面解决跨域

Apache

<IfModule mod_headers.c>

<FilesMatch "\.(svg|ttf|otf|eot|woff|woff2)$">

Header set Access-Control-Allow-Origin "*"

</FilesMatch>

</IfModule>

Nginx

location ~* \.(eot|ttf|woff)$ {

   add_header Access-Control-Allow-Origin '*';

}

Access-Control-Allow-Origin:* 表示允许任何域名跨域访问。

扩展

server {

  listen        80;

  server_name   uedbox.com;

  location / {

    # Simple requests

    if ($request_method ~* "(GET|POST)") {

      add_header "Access-Control-Allow-Origin"  *;

    }

    # Preflighted requests

    if ($request_method = OPTIONS ) {

      add_header "Access-Control-Allow-Origin"  *;

      add_header "Access-Control-Allow-Methods" "GET, POST, OPTIONS, HEAD";

      add_header "Access-Control-Allow-Headers" "Authorization, Origin, X-Requested-With, Content-Type, Accept";

      return 200;

    }

    ....

    # Handle request

    ....

  }

}

你还可以动态配置跨域方案

set $cors '';

if ($http_origin ~ '^https?://(localhost|www\.yourdomain\.com|www\.yourotherdomain\.com)') {
     set $cors 'true';
}

if ($cors = 'true') {

        add_header 'Access-Control-Allow-Origin' "$http_origin" always;

        add_header 'Access-Control-Allow-Credentials' 'true' always;

        add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS' always;

        add_header 'Access-Control-Allow-Headers' 'Accept,Authorization,Cache-Control,Content-Type,DNT,If-Modified-Since,Keep-Alive,Origin,User-Agent,X-Requested-With' always;

        # required to be able to read Authorization header in frontend

        #add_header 'Access-Control-Expose-Headers' 'Authorization' always;

}

if ($request_method = 'OPTIONS') {

        # Tell client that this pre-flight info is valid for 20 days

        add_header 'Access-Control-Max-Age' 1728000;

        add_header 'Content-Type' 'text/plain charset=UTF-8';

        add_header 'Content-Length' 0;

        return 204;

}

代码配置解决跨域

PHP

<?php

if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    header("Access-Control-Allow-Origin: *");
    header("Access-Control-Allow-Methods: GET, POST, OPTIONS");
    header("Access-Control-Allow-Headers: Content-Type");
    exit;
}

$ret = array(
    'name' => isset($_POST['name'])? $_POST['name'] : '',
    'gender' => isset($_POST['gender'])? $_POST['gender'] : ''
);

header('content-type:application:json;charset=utf8');
header('Access-Control-Allow-Origin:*');
header('Access-Control-Allow-Methods:POST');
header('Access-Control-Allow-Headers:x-requested-with,content-type');

echo json_encode($ret);

如果需要指定某域名才允许跨域访问，只需把Access-Control-Allow-Origin:*改为Access-Control-Allow-Origin:允许的域名，例如：

header('Access-Control-Allow-Origin:https://www.xiadmin.com');

如果需要设置多个域名允许访问，那么把多个域名放在数组中就可以，例如：

<?php

$ret = array(

    'name' => isset($_POST['name'])? $_POST['name'] : '',

    'gender' => isset($_POST['gender'])? $_POST['gender'] : ''

);
header('content-type:application:json;charset=utf8');
$origin = isset($_SERVER['HTTP_ORIGIN'])? $_SERVER['HTTP_ORIGIN'] : '';

$allow_origin = array(
    'https://www.xiadmin.com',
    'https://www.xiadmin.com'
);

if(in_array($origin, $allow_origin)){
    header('Access-Control-Allow-Origin:'.$origin);
    header('Access-Control-Allow-Methods:POST');
    header('Access-Control-Allow-Headers:x-requested-with,content-type');
}

echo json_encode($ret);

No ‘Access-Control-Allow-Origin’问题解决！