Usage:

system.Exec("curl -sSu 'ccu3:Essel-54' https://smartthings.home.ttlx.de/monitor/on &");

system.Exec("curl -sSu 'ccu3:Essel-54' https://smartthings.home.ttlx.de/monitor/off &");

string action = "on";
string stdout;
string stderr;
string cmd = "curl -sSu 'ccu3:Essel-54' https://smartthings.home.ttlx.de/monitor/" # action;
system.Exec(cmd, &stdout, &stderr);