[#1379] neofs-cli: Add key.GetOrGenerate helper

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

cmd/neofs-cli/internal/key/raw.go

@@ -2,6 +2,7 @@ package key
 
 import (
 	"crypto/ecdsa"
+	"errors"
 	"fmt"
 	"os"
 
@@ -11,6 +12,8 @@ import (
 	"github.com/spf13/viper"
 )
 
+var errCantGenerateKey = errors.New("can't generate new private key")
+
 // Get returns private key from the following sources:
 // 1. WIF
 // 2. Raw binary key
@@ -43,6 +46,18 @@ func Get() (*ecdsa.PrivateKey, error) {
 	return nil, ErrInvalidKey
 }
 
+// GetOrGenerate is similar to get but generates a new key if commonflags.GenerateKey is set.
+func GetOrGenerate() (*ecdsa.PrivateKey, error) {
+	if viper.GetBool(commonflags.GenerateKey) {
+		priv, err := keys.NewPrivateKey()
+		if err != nil {
+			return nil, fmt.Errorf("%w: %v", errCantGenerateKey, err)
+		}
+		return &priv.PrivateKey, nil
+	}
+	return Get()
+}
+
 func getKeyFromFile(keyPath string) (*ecdsa.PrivateKey, error) {
 	data, err := os.ReadFile(keyPath)
 	if err != nil {