Only in production, and never on localhost, superagent seems to made additional GET request right before POST requests. This is similar to this unanswered question however that was using other software, this is simply superagent.
The client code is simple a POST request:
superagent
.post('/api/v1/csr/whois')
.send({
someKey: someValue
})
.end(function(res){
log('Whois response:', res)
})