Add ReadPasswordBytes for crypto use cases

Returns []byte so callers can zeroize the buffer after use.
Refactors internals to share readRaw between both variants.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

terminal/terminal.go

@@ -12,11 +12,25 @@ import (
 // from the terminal with echo disabled. It prints a newline after the
 // input is complete so the cursor advances normally.
 func ReadPassword(prompt string) (string, error) {
-	fmt.Fprint(os.Stderr, prompt)
-	b, err := term.ReadPassword(int(os.Stdin.Fd())) //nolint:gosec // fd fits in int
-	fmt.Fprintln(os.Stderr)
+	b, err := readRaw(prompt)
 	if err != nil {
 		return "", err
 	}
 	return string(b), nil
 }
+
+// ReadPasswordBytes is like ReadPassword but returns a []byte so the
+// caller can zeroize the buffer after use.
+func ReadPasswordBytes(prompt string) ([]byte, error) {
+	return readRaw(prompt)
+}
+
+func readRaw(prompt string) ([]byte, error) {
+	fmt.Fprint(os.Stderr, prompt)
+	b, err := term.ReadPassword(int(os.Stdin.Fd())) //nolint:gosec // fd fits in int
+	fmt.Fprintln(os.Stderr)
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}

terminal/terminal_test.go

@@ -12,3 +12,10 @@ func TestReadPasswordNotATTY(t *testing.T) {
 		t.Fatal("expected error when stdin is not a terminal")
 	}
 }
+
+func TestReadPasswordBytesNotATTY(t *testing.T) {
+	_, err := ReadPasswordBytes("Password: ")
+	if err == nil {
+		t.Fatal("expected error when stdin is not a terminal")
+	}
+}