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).