request logging profile want to log client certificate details

tmsh create ltm profile request-log ybrequest-log-20220126
tmsh modify ltm profile request-log ybrequest-log-20220126 app-service none defaults-from ybrequest-log \
#
#request-log-template '$BIGIP_HOSTNAME , $VIRTUAL_NAME , "$\{Host\}",RQ,$CLIENT_IP,$CLIENT_PORT,$DATE_NCSA,$HTTP_METHOD,$HTTP_URI,$HTTP_VERSION,\"${User-agent}\",\"${X-Forwarded-SSL-cert-subject}\","$\{YBID\}","$\{ybmethod\}","$\{DEBTSTHREAD\}"' \
#response-log-template '$BIGIP_HOSTNAME , $VIRTUAL_NAME , "$\{Host\}",RS,$CLIENT_IP,$CLIENT_PORT,$DATE_NCSA,$HTTP_METHOD,$HTTP_URI,$HTTP_VERSION,\"${User-agent}\",\"${X-Forwarded-SSL-cert-subject}\","$\{YBID\}","$\{ybmethod\}","$\{DEBTSTHREAD\}",$VIRTUAL_POOL_NAME,$SERVER_IP,$SERVER_PORT,$SNAT_IP,$SNAT_PORT,$HTTP_STATCODE,$RESPONSE_SIZE,$RESPONSE_MSECS,"$\{X-time\}"'
#

is the header added by the irule

X-Forwarded-SSL-cert-subject

the irule looks something like 

set certsubject [X509::subject $cert]
HTTP::header insert X-Forwarded-SSL-DN $certsubject

Not sure why thus makes a difference. The general question is how to log client cert info in request-log