Additional way to configure in F5 header X-SSL-Client-DN

This is not recommended (it can be used if iRules can not be defined in F5) because only one header can be inserted (X-Forwarded-For can not be inserted).

Only one header can be added in this way (the application works also without the proxy secret, that is inserted in haproxy).

X-SSL-Client-DN: [X509::subject [SSL::cert 0]]