wso2mi 4.1 - Get CN from an X509 certificate for XACML subject-id

Question

I followed applying security to a proxy service article. My problem is that in the XACML request the subject-id property value is an LDAP query "CN=localhost, OU=WSO2, O=WSO2, L=Mountain View, ST=CA, C=US". what should I do to just commonName (CN) value become subject-id?

My entitlement mediator:

<entitlementService 
 callbackClass="org.wso2.micro.integrator.identity.entitlement.mediator.callback.X509EntitlementCallbackHandler"
 remoteServiceUrl=" https://testdomain.org:9444/services/" 
 client="basicAuth" 
 remoteServicePassword="admin" 
 remoteServiceUserName="admin">

XACML request that entitlement mediator made:

<Request xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" CombinedDecision="false" ReturnPolicyIdList="false">
<Attributes Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">
CN=localhost, OU=WSO2, O=WSO2, L=Mountain View, ST=CA, C=US
</AttributeValue></Attribute></Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">
read
</AttributeValue></Attribute></Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:resource">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">
/services/SecureProxy/createUser
</AttributeValue></Attribute></Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:environment">
<Attribute AttributeId="IssuerDN" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">
CN=localhost, OU=WSO2, O=WSO2, L=Mountain View, ST=CA, C=US
</AttributeValue></Attribute>
<Attribute AttributeId="SignatureAlgorithm" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">
SHA256withRSA
</AttributeValue></Attribute></Attributes></Request>

WSO2 Micro Integrator 4.1, Identity Server 5.11, and SoapUI 5.7.0.