Adding Information to SOAP Header

<xsl:stylesheet version="1.0" 
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
 <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
 <xsl:strip-space elements="*"/>
 
<xsl:template match="@*|node()">
     <xsl:copy>
         <xsl:apply-templates select="@*|node()"/>
     </xsl:copy>
 </xsl:template>
 
 <xsl:template match="/soapenv:Envelope">
     <xsl:copy>
       <soapenv:Header>
          <UserName xmlns="apinizer.com">Test123</UserName>
       </soapenv:Header>
         <xsl:apply-templates/>
     </xsl:copy>
 </xsl:template>
 
 <xsl:template match="soapenv:Header"/>
 
 </xsl:stylesheet>
XML