Add Pinentry CLI fallback (gopasspw#1697)

Fixes gopasspw#1655

RELEASE_NOTES=[ENHANCEMENT] Add Pinentry CLI fallback

Signed-off-by: Dominik Schulz <dominik.schulz@gauner.org>

internal/backend/crypto/age/askpass.go

@@ -8,6 +8,7 @@ import (
 	"github.com/gopasspw/gopass/internal/cache"
 	"github.com/gopasspw/gopass/pkg/debug"
 	"github.com/gopasspw/gopass/pkg/pinentry"
+	"github.com/gopasspw/gopass/pkg/pinentry/cli"
 )
 
 type piner interface {
@@ -38,7 +39,12 @@ func newAskPass() *askPass {
 	return &askPass{
 		cache: cache.NewInMemTTL(time.Hour, 24*time.Hour),
 		pinentry: func() (piner, error) {
-			return pinentry.New()
+			p, err := pinentry.New()
+			if err == nil {
+				return p, nil
+			}
+			debug.Log("Pinentry not found: %q", err)
+			return cli.New()
 		},
 	}
 }

pkg/pinentry/cli/fallback.go

@@ -0,0 +1,42 @@
+package cli
+
+import (
+	"context"
+
+	"github.com/gopasspw/gopass/pkg/termio"
+)
+
+// Client is pinentry CLI drop-in
+type Client struct{}
+
+// New creates a new client
+func New() (*Client, error) {
+	return &Client{}, nil
+}
+
+// Close is a no-op
+func (c *Client) Close() {}
+
+// Confirm is a no-op
+func (c *Client) Confirm() bool {
+	return true
+}
+
+// Set is a no-op
+func (c *Client) Set(string, string) error {
+	return nil
+}
+
+// Option is a no-op
+func (c *Client) Option(string) error {
+	return nil
+}
+
+// GetPin prompts for the pin in the termnial and returns the output
+func (c *Client) GetPin() ([]byte, error) {
+	pw, err := termio.AskForPassword(context.TODO(), "Please enter your PIN")
+	if err != nil {
+		return nil, err
+	}
+	return []byte(pw), nil
+}