It is clear how to get the request header value with a specific name:
Class My.RestController Extends %CSP.REST
{
ClassMethod processRequest() As %Status
{
#dim request as %CSP.Request
set request = %request
set h = ##class(%REST.Impl).%GetHeader("...")
...
return $$$OK
}
But I can't figure out how to enumerate ALL the request headers (and also get all values).