Fix XSS (CVE-2020-5497)

[irbishop]

Fix for #1521

#1526 was on the right track - escapeXml works for the instances in topbar.tag because individual values are referenced from userInfo:

						<li class="dropdown">
							<a id="userButton" class="dropdown-toggle" data-toggle="dropdown" href=""><i class="icon-user icon-white"></i> user <span class="caret"></span></a>
							<ul class="dropdown-menu pull-right">
								<li><a href="manage/#user/profile" data-toggle="collapse" data-target=".nav-collapse">Demo &lt;script&gt;alert(1)&lt;/script&gt;User</a></li>
								<li class="divider"></li>
								<li><a href="" data-toggle="collapse" data-target=".nav-collapse" class="logoutLink"><i class="icon-remove"></i> Log out</a></li>
							</ul>
						</li>
	                    
	                    
	                </ul>
	                
	                <!--  use a simplified user button system when collapsed -->
	                <ul class="nav hidden-desktop">
	                    
						<li><a href="manage/#user/profile">Demo &lt;script&gt;alert(1)&lt;/script&gt;User</a></li>
						<li class="divider"></li>
						<li><a href="" class="logoutLink"><i class="icon-remove"></i> Log out</a></li>
	                    
	                    
	                </ul>

Using escapeXml on userInfoJson in header.tag breaks the JSON:

Reference image

I looked at UseInforInterceptor, so using custom UserInfo will be protected as well. It's the simplest way I could think of:

• Convert the response from UserInfo.toJson to JsonElement
• Dump the JsonElement with gson

The result is userInfoJson appearing like:

   	function getUserInfo() {
    		return {"sub":"01921.FLANRJQW","name":"Demo \u003cscript\u003ealert(1)\u003c/script\u003eUser","preferred_username":"user","email":"user@example.com","email_verified":true};
    	}