Exaple request and response:
NOTE: by arrow marked fields which need to hide for example
You would probably need to make your own middleware script to request from cockpit, filter, and return.
You do not need a middleware… You can just create api endpoints (which are reflected onto a php-script) a very simple way:
Ok. Thank you! I will try, although I am not php developer 
I thought it configurable in the cockpit.
Ok. Thanks for modest answer I thought, it can be filtering inside “fields” POST body. For example:
{
“fields”: {
“active”: 0,
“tests.active”: 0
or
“tests”: {
“active”: 0
}
},
“populate”: 1
}
so, software in the middle 