render context: add asset_download_token

cmd/dkl-local-server/render-context.go

@@ -14,6 +14,7 @@ import (
 	"path"
 	"path/filepath"
 	"text/template"
+	"time"
 
 	cfsslconfig "github.com/cloudflare/cfssl/config"
 	restful "github.com/emicklei/go-restful"
@@ -237,6 +238,32 @@ func (ctx *renderContext) TemplateFuncs() map[string]any {
 				}
 			}
 
+			return
+		},
+		"asset_download_token": func(asset string, params ...string) (token string, err error) {
+			now := time.Now()
+			exp := now.Add(24 * time.Hour) // expire in 24h by default
+			if len(params) != 0 {
+				exp, err = parseCertDuration(params[0], now)
+				if err != nil {
+					return
+				}
+			}
+
+			set := DownloadSet{
+				Expiry: exp,
+				Items: []DownloadSetItem{
+					{
+						Kind:   "host",
+						Name:   ctx.Host.Name,
+						Assets: []string{asset},
+					},
+				},
+			}
+
+			privKey, _ := dlsSigningKeys()
+			token = set.Signed(privKey)
+
 			return
 		},
 	} {