try this
<xsl:variable name="client_id" select="'bla-043C-654-F654-534'"/>
<xsl:variable name="client_secret" select="'ABCD234-654-654DK-BC-498646'"/>
<xsl:variable name="grant_type" select="'client_credentials'"/>
<xsl:variable name="POST">
<xsl:text>client_id=</xsl:text>
<xsl:value-of select="$client_id" disable-output-escaping="yes"/>
<xsl:text>&client_secret=</xsl:text>
<xsl:value-of select="$client_secret" disable-output-escaping="yes"/>
<xsl:text>grant_type=</xsl:text>
<xsl:value-of select="$grant_type" disable-output-escaping="yes"/>
</xsl:variable>
<xsl:variable name="url" select="'https://someweb.com/data/v1/oauth2/token'"/>
<xsl:variable name="callServeurAuth">
<dp:url-open target="{$url}" response="responsecode-binary" content-type="application/x-www-form-urlencoded" ssl-proxy="BACK_SSL" http-method="POST" data-type="base64">
<xsl:value-of select="dp:encode($POST, 'base-64')"/>
</dp:url-open>
</xsl:variable>
<xsl:copy-of select="dp:stringToJSONx(dp:decode(dp:binary-encode($callServeurAuth/result/binary/node()),'base-64'))"/>
<!--<xsl:copy-of select="dp:binaryNodeToJSONx(dp:binary-decode(dp:binary-encode($callServeurAuth/result/binary/node())))"/>-->
#DataPower#Support#SupportMigration