I want to add

Access-Control-Allow-Headers:DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type

but in response I got

Access-Control-Allow-Headers:DNT

if I specify

Access-Control-Allow-Headers:"DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type"

I got
Access-Control-Allow-Headers:"DNT

for
Access-Control-Allow-Headers:'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type'

I got
Access-Control-Allow-Headers:'DNT