Here is my XSLT, where you can see where I need to pass the value.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xsl:stylesheet [ <!ENTITY nbsp "&#x00A0;"> ]>
<xsl:stylesheet 
  version="1.0" 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:msxml="urn:schemas-microsoft-com:xslt"
  xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltCommon="urn:Exslt.ExsltCommon" xmlns:Exslt.ExsltDatesAndTimes="urn:Exslt.ExsltDatesAndTimes" xmlns:Exslt.ExsltMath="urn:Exslt.ExsltMath" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" xmlns:Exslt.ExsltStrings="urn:Exslt.ExsltStrings" xmlns:Exslt.ExsltSets="urn:Exslt.ExsltSets" xmlns:Designit.VideoEmbed="urn:Designit.VideoEmbed" xmlns:ucomponents.cms="urn:ucomponents.cms" xmlns:ucomponents.dates="urn:ucomponents.dates" xmlns:ucomponents.io="urn:ucomponents.io" xmlns:ucomponents.media="urn:ucomponents.media" xmlns:ucomponents.members="urn:ucomponents.members" xmlns:ucomponents.nodes="urn:ucomponents.nodes" xmlns:ucomponents.search="urn:ucomponents.search" xmlns:ucomponents.strings="urn:ucomponents.strings" xmlns:ucomponents.urls="urn:ucomponents.urls" xmlns:ucomponents.xml="urn:ucomponents.xml" xmlns:PS.XSLTsearch="urn:PS.XSLTsearch" 
  exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets Designit.VideoEmbed ucomponents.cms ucomponents.dates ucomponents.io ucomponents.media ucomponents.members ucomponents.nodes ucomponents.search ucomponents.strings ucomponents.urls ucomponents.xml PS.XSLTsearch ">


<xsl:output method="html" omit-xml-declaration="yes"/>

<xsl:param name="currentPage"/>

<xsl:template match="/">

  <xsl:if test="$currentPage/ancestor-or-self::* [activeMenu = 'Lawyers' or @id=1672]">
    <script type="text/javascript" src="/js/jquery.ba-postmessage.min.js"></script>
    <script type="text/javascript">
      $(function(){
 
        // Pass the parent page URL into the Iframe in a meaningful way (this URL could be
        // passed via query string or hard coded into the child page, it depends on your needs).
        var src = 'http://<xsl:value-of select="umbraco.library:Replace(umbraco.library:RequestServerVariables('SERVER_NAME'),'.azbar.','.myazbar.')" />/includes/logInOut_btn_iFramed.cfm#' + encodeURIComponent(document.location.href),
      // Append the Iframe into the DOM.
      iframe = $('<iframe src="' + src + '" name="logInOut_btn_iframe" id="logInOut_btn_iframe" width="200" height="32" frameborder="0" allowtransparency="yes" marginheight="0"
      marginwidth="0" scrolling="no" class="btn-login-iFrame"></iframe>')
        .appendTo('#theIFrame');
      
      // Setup a callback to handle the dispatched MessageEvent event. In cases where
      // window.postMessage is supported, the passed event will have .data, .origin and
      // .source properties. Otherwise, this will only have the .data property.
      $.receiveMessage(function(e){
    
      alert("XSLT: " + e.data);
      
      if (e.data=="loggedIn=yes") {
        isLoggedIn = "Yes";
      }
      else if (e.data == "loggedIn=no") {
        isLoggedIn = "No";
      }
      
      // ***** SEND isLoggedIn VALUE TO WEB SERVICE
      //SBA.AZBar.UserControls.SetLoggedInStatus.setStatus(isLoggedIn);
     
        // An optional origin URL (Ignored where window.postMessage is unsupported).
      }, 'http://<xsl:value-of select="umbraco.library:Replace(umbraco.library:RequestServerVariables('SERVER_NAME'),'.azbar.','.myazbar.')" />' );
    
      });
    </script>
  </xsl:if>
  
  <span id="theIFrame"></span>

</xsl:template>

</xsl:stylesheet>

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