reverseproxy: add Max-Age option to sticky cookie (#6398)

* reverseproxy: add Max-Age option to sticky cookie

* Update selectionpolicies.go

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

* Update selectionpolicies.go

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

---------

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

modules/caddyhttp/reverseproxy/selectionpolicies.go

@@ -26,6 +26,7 @@ import (
 	"strconv"
 	"strings"
 	"sync/atomic"
+	"time"
 
 	"github.com/cespare/xxhash/v2"
 
@@ -613,6 +614,8 @@ type CookieHashSelection struct {
 	Name string `json:"name,omitempty"`
 	// Secret to hash (Hmac256) chosen upstream in cookie
 	Secret string `json:"secret,omitempty"`
+	// The cookie's Max-Age before it expires. Default is no expiry.
+	MaxAge caddy.Duration `json:"max_age,omitempty"`
 
 	// The fallback policy to use if the cookie is not present. Defaults to `random`.
 	FallbackRaw json.RawMessage `json:"fallback,omitempty" caddy:"namespace=http.reverse_proxy.selection_policies inline_key=policy"`
@@ -671,6 +674,9 @@ func (s CookieHashSelection) Select(pool UpstreamPool, req *http.Request, w http
 			cookie.Secure = true
 			cookie.SameSite = http.SameSiteNoneMode
 		}
+		if s.MaxAge > 0 {
+			cookie.MaxAge = int(time.Duration(s.MaxAge).Seconds())
+		}
 		http.SetCookie(w, cookie)
 		return upstream
 	}
@@ -699,6 +705,7 @@ func (s CookieHashSelection) Select(pool UpstreamPool, req *http.Request, w http
 //
 //	lb_policy cookie [<name> [<secret>]] {
 //		fallback <policy>
+//		max_age <duration>
 //	}
 //
 // By default name is `lb`
@@ -728,6 +735,24 @@ func (s *CookieHashSelection) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				return err
 			}
 			s.FallbackRaw = mod
+		case "max_age":
+			if !d.NextArg() {
+				return d.ArgErr()
+			}
+			if s.MaxAge != 0 {
+				return d.Err("cookie max_age already specified")
+			}
+			maxAge, err := caddy.ParseDuration(d.Val())
+			if err != nil {
+				return d.Errf("invalid duration: %s", d.Val())
+			}
+			if maxAge <= 0 {
+				return d.Errf("invalid duration: %s, max_age should be non-zero and positive", d.Val())
+			}
+			if d.NextArg() {
+				return d.ArgErr()
+			}
+			s.MaxAge = caddy.Duration(maxAge)
 		default:
 			return d.Errf("unrecognized option '%s'", d.Val())
 		}