I’d like to receive passive check results directly on an agent. Therefore I need to configure an API user on the agent. Is that possible using Icinga Director?
If yes, how? 
is it just one check or do you need result for all checks?
I would suggest that you modify your check to write the result directly to disk.
you could create an api user on the icinga master node and query the check result with the icinga api once it’s transmitted
https://icinga.com/docs/icinga-2/latest/doc/12-icinga2-api/