authres: Put 'reason' before other properies

authres/format.go

@@ -49,9 +49,15 @@ func resultMethod(r Result) string {
 func formatParams(params map[string]string) string {
 	keys := make([]string, 0, len(params))
 	for k := range params {
+		if k == "reason" {
+			continue
+		}
 		keys = append(keys, k)
 	}
 	sort.Strings(keys)
+	if params["reason"] != "" {
+		keys = append([]string{"reason"}, keys...)
+	}
 
 	s := ""
 	i := 0

authres/msgauth_test.go

@@ -20,6 +20,14 @@ var msgauthTests = []msgauthTest{
 			&SPFResult{Value: ResultPass, From: "example.net"},
 		},
 	},
+	{
+		value: "example.com;" +
+			" spf=fail reason=bad smtp.mailfrom=example.net",
+		identifier: "example.com",
+		results: []Result{
+			&SPFResult{Value: ResultFail, Reason: "bad", From: "example.net"},
+		},
+	},
 	{
 		value: "example.com;" +
 			" auth=pass [email protected];" +