Hi,
You can send it in HTTP header.
ROIndyHTTPChannel1.IndyClient.Request.CustomHeaders.AddValue('myheader','myvalue');
on server-side you can read it in Service.OnGetDispatchInfo event:
procedure TNewProjectService.RORemoteDataModuleGetDispatchInfo(
const aTransport: IROTransport; const aMessage: IROMessage);
var
s: string;
begin
s := (aTransport as IROHTTPTransport).Headers['myheader'];
end;
if you like to pass user credential and process it before execution of service method, you can use HTTPServer.OnCustomResponseEvent event.
check for more info in Using OnCustomResponseEvent in a ROSDK Server snippet.