A站(www.a.com)，有个form表单，ajax提交到 B站(www.b.com)，还附带个验证码。

A站上的表单代码如下：

<script type="text/javascript" src="/d/file/2019/11/03/3234.html send(){    $.ajax({        cache:true,        type:"POST",        url:"http://www.b.com/plus/diy.php",        data:$('#diyform').serialize(),        xhrFields:{withCredentials: true}, //ajax跨域提交需要        crossDomain:true, //ajax跨域提交需要        success: function(data){            if(data=="success"){                alert('发送成功!');            }else{                alert('发送失败!');            }        }    });}</script><form action="" enctype="multipart/form-data" method="post" id="diyform">    <input type="hidden" name="action" value="post" />    <input type="hidden" name="diyid" value="2" />    <input type="hidden" name="do" value="2" />    <input type="hidden" name="dede_fields" value="name,text" />    <input type="hidden" name="dede_fieldshash" value="c2be5bb5ec45d9d01ca9f60dc469b3fb" />    <p>        姓名：        <input type='text' name='name' id='name' />    </p>    <p>        验证码：        <input type="text" name="validate"><img src="http://www.b.com/include/vdimgck.php" align="absmiddle" onclick="this.src='http://www.b.com/include/vdimgck.php?tag='+Math.random();" style="cursor:pointer;">    </p>    <div onclick="send()">提交</div></form>

1、提交到 http://www.b.com/plus/diy.php

2、验证码 http://www.b.com/include/vdimgck.php

3、ajax 跨域必需js代码

xhrFields:{withCredentials: true},

crossDomain:true,

B站上的 /plus/diy.php 文件上面加入

header("Access-Control-Allow-Credentials:true");

header("Access-Control-Allow-Origin:http://www.a.com");