feat: add pass_thru mode to continue to next handler instead of replying directly (#23)

Thank you @adrienyhuel for contributing.
Merged now

Author: adrienyhuel

README.adoc

@@ -102,6 +102,9 @@ The default size is **1G**.
 |**dest_dir_field_name**
 |If set, the dest_dir will be set from the specified form value.
 
+|**pass_thru**
+|If set to `true`, enables pass-thru mode, which continues to the next HTTP handler in the route instead of responding directly.
+
 |===
 
 === Caddy Variables

caddyfile.go

@@ -107,6 +107,16 @@ func (u *Upload) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				if !d.Args(&u.DestDirFieldName) {
 					return d.ArgErr()
 				}
+			case "pass_thru":
+				var passThruStr string
+				if !d.AllArgs(&passThruStr) {
+					return d.ArgErr()
+				}
+				passThruBool, err := strconv.ParseBool(passThruStr)
+				if err != nil {
+					return d.Errf("parsing pass_thru: %v", err)
+				}
+				u.PassThru = passThruBool
 			default:
 				return d.Errf("unrecognized servers option '%s'", d.Val())
 			}

upload.go

@@ -40,6 +40,7 @@ type Upload struct {
 	NotifyMethod     string `json:"notify_method,omitempty"`
 	CreateUuidDir    bool   `json:"create_uuid_dir,omitempty"`
 	DestDirFieldName string `json:"dest_dir_field_name,omitempty"`
+	PassThru         bool   `json:"pass_thru,omitempty"`
 
 	MyTlsSetting struct {
 		InsecureSkipVerify bool   `json:"insecure,omitempty"`
@@ -173,6 +174,7 @@ func (u *Upload) Provision(ctx caddy.Context) error {
 		zap.String("capath", u.MyTlsSetting.CAPath),
 		zap.Bool("insecure", u.MyTlsSetting.InsecureSkipVerify),
 		zap.String("dest_dir_field_name", u.DestDirFieldName),
+		zap.Bool("pass_thru", u.PassThru),
 	)
 
 	return nil
@@ -326,6 +328,10 @@ func (u Upload) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp
 		}
 	}
 
+	if u.PassThru {
+		return next.ServeHTTP(w, r)
+	}
+
 	if u.ResponseTemplate != "" {
 
 		fileRespTemplate, fRTErr := os.Open(caddyhttp.SanitizedPathJoin(u.RootDir, u.ResponseTemplate))