internal/plugin,cmd/age: implement confirm protocol verb

cmd/age/parse.go

@@ -37,6 +37,7 @@ func parseRecipient(arg string) (age.Recipient, error) {
 		}
 		r.DisplayMessage = pluginDisplayMessage(r.Name())
 		r.RequestValue = pluginRequestSecret(r.Name())
+		r.Confirm = pluginConfirm(r.Name())
 		return r, nil
 	case strings.HasPrefix(arg, "age1"):
 		return age.ParseX25519Recipient(arg)
@@ -210,6 +211,7 @@ func parseIdentity(s string) (age.Identity, error) {
 		}
 		i.DisplayMessage = pluginDisplayMessage(i.Name())
 		i.RequestValue = pluginRequestSecret(i.Name())
+		i.Confirm = pluginConfirm(i.Name())
 		return i, nil
 	case strings.HasPrefix(s, "AGE-SECRET-KEY-1"):
 		return age.ParseX25519Identity(s)

cmd/age/tui.go

@@ -18,6 +18,7 @@ import (
 	"log"
 	"os"
 	"runtime"
+	"strings"
 
 	"golang.org/x/term"
 )
@@ -111,3 +112,30 @@ func pluginRequestSecret(name string) func(string, bool) (string, error) {
 		return string(secret), nil
 	}
 }
+
+func pluginConfirm(name string) func(msg, yes, no string) (bool, error) {
+	return func(message, yes, no string) (bool, error) {
+		if no != "" {
+			message += fmt.Sprintf(" (1 for %q, 2 for %q)", yes, no)
+			selection, err := readSecret(message)
+			if err != nil {
+				return false, fmt.Errorf("could not read value for age-plugin-%s: %v", name, err)
+			}
+			switch strings.TrimSpace(string(selection)) {
+			case "1":
+				return true, nil
+			case "2":
+				return false, nil
+			default:
+				return false, fmt.Errorf("invalid selection %q", selection)
+			}
+		} else {
+			message += fmt.Sprintf(" (press enter for %q)", yes)
+			_, err := readSecret(message)
+			if err != nil {
+				return false, fmt.Errorf("could not read value for age-plugin-%s: %v", name, err)
+			}
+			return true, nil
+		}
+	}
+}