1. As header (recommended, possible without SSL) with "-H" option
curl -H "X-ReportServer-ClientID: apiuser1" -H "X-ReportServer-ClientToken: y8kUirLTXL+KIl7tDXptvvu11WFB9yfn" "http://combitreportserver/api/....."
2. As URL parameter (only possible with SSL)
curl "https://combitreportserver/api/.....?clientid=apiuser123& clienttoken=y8kUirLTXL+KIl7tDXptvvu11WFB9yfn"