The requested URL could not be retrieved

在开发过程中，调用对外接口，返回了一长串的标签提示，如下
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head>
<meta type="copyright" content="Copyright (C) 1996-2017 The Squid Software Foundation and contributors">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>ERROR: The requested URL could not be retrieved</title>
<style type="text/css"><!--
 /*
 * Copyright (C) 1996-2017 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */

/*
 Stylesheet for Squid Error pages
 Adapted from design by Free CSS Templates
 http://www.freecsstemplates.org
 Released for free under a Creative Commons Attribution 2.5 License
*/

/* Page basics */
* {
    font-family: verdana, sans-serif;
}

html body {
    margin: 0;
    padding: 0;
    background: #efefef;
    font-size: 12px;
    color: #1e1e1e;
}

/* Page displayed title area */
#titles {
    margin-left: 15px;
    padding: 10px;
    padding-left: 100px;
    background: url('/squid-internal-static/icons/SN.png') no-repeat left;
}

/* initial title */
#titles h1 {
    color: #000000;
}
#titles h2 {
    color: #000000;
}

/* special event: FTP success page titles */
#titles ftpsuccess {
    background-color:#00ff00;
    100%;
}

/* Page displayed body content area */
#content {
    padding: 10px;
    background: #ffffff;
}

/* General text */
p {
}

/* error brief description */
#error p {
}

/* some data which may have caused the problem */
#data {
}

/* the error message received from the system or other software */
#sysmsg {
}

pre {
    font-family:sans-serif;
}

/* special event: FTP / Gopher directory listing */
#dirmsg {
    font-family: courier;
    color: black;
    font-size: 10pt;
}
#dirlisting {
    margin-left: 2%;
    margin-right: 2%;
}
#dirlisting tr.entry td.icon,td.filename,td.size,td.date {
    border-bottom: groove;
}
#dirlisting td.size {
     50px;
    text-align: right;
    padding-right: 5px;
}

/* horizontal lines */
hr {
    margin: 0;
}

/* page displayed footer area */
#footer {
    font-size: 9px;
    padding-left: 10px;
}


body
:lang(fa) { direction: rtl; font-size: 100%; font-family: Tahoma, Roya, sans-serif; float: right; }
:lang(he) { direction: rtl; }
 --></style>
</head><body id=ERR_ACCESS_DENIED>
<div id="titles">
<h1>ERROR</h1>
<h2>The requested URL could not be retrieved</h2>
</div>
<hr>

<div id="content">
<p>The following error was encountered while trying to retrieve the URL: <a href="https://cloud.zdns.cn/*">https://cloud.zdns.cn/*</a></p>

<blockquote id="error">
<p><b>Access Denied.</b></p>
</blockquote>

<p>Access control configuration prevents your request from being allowed at this time. 
Please contact your service provider if you feel this is incorrect.</p>

<p>Your cache administrator is
 <a href="mailto:webmaster?subject=CacheErrorInfo%20-%20ERR_ACCESS_DENIED&amp;
 body=CacheHost%3A%20xzproxy01%0D%0AErrPage%3A%20ERR_ACCESS_DENIED%0D%0AErr%3A%20%
 5Bnone%5D%0D%0ATimeStamp%3A%20Fri,%2013%20Mar%202020%2002%3A56%3A20%20GMT%0D%0A%0D%
 0AClientIP%3A%2010.49.9.125%0D%0A%0D%0AHTTP%20Request%3A%0D%0ACONNECT%20%2F%20HTTP%2F1.1%0
 AUser-Agent%3A%20Apache-HttpClient%2F4.5.2%20(Java%2F1.8.0_181)%0D%0AHost%3A%20cloud.zdns.c
 n%3A443%0D%0A%0D%0A%0D%0A">webmaster</a>.</p>
<br>
</div>

<hr>
<div id="footer">
<p>Generated Fri, 13 Mar 2020 02:56:20 GMT by xzproxy01 (squid/3.5.25)</p>
<!-- ERR_ACCESS_DENIED -->
</div>
</body></html>
　　该提示之后，发现请求不通，代理服务器拦截了这个请求，squid是代理服务器控制软件。在网上搜了下，看到一篇不错的文章，
链接如下，用于扩充吧
The requested URL could not be retrieved/ TCP_DENIED/403
