F5 require client certificate to forward to a backend server only in specific uri

Something like that should do it :

https://clouddocs.f5.com/api/irules/ClientCertificateCNChecking.html

For example, taken from this page :

when RULE_INIT {
        set static::debug 1
}
 
when CLIENTSSL_CLIENTCERT {
        #Example Subject DN:  /C=AU/ST=NSW/L=Syd/O=Your Organisation/OU=Your OU/CN=John Smith
        set subject_dn [X509::subject [SSL::cert 0]]
        if { $subject_dn != "" }{
                if { $static::debug }{ log "Client Certificate received: $subject_dn"}
        }
}
when HTTP_REQUEST {
        if { [HTTP::uri] starts_with "/companyA" } {
                if { !($subject_dn contains "CN=Company A") } {
                        reject
                }
        } elseif { [HTTP::uri] starts_with "/companyB" } {
                if { !($subject_dn contains "CN=Company B") } {
                        reject
                }
        }
}