Add S3-compatible storage backend

internal/config/secrets.go

@@ -80,6 +80,9 @@ func (e Environment) required(name string) (string, error) {
 	if !ok {
 		return "", fmt.Errorf("credential environment variable %s is not set", name)
 	}
+	if value == "" {
+		return "", fmt.Errorf("credential environment variable %s is empty", name)
+	}
 	return value, nil
 }