Index: flexoentity/domain.py
===================================================================
--- flexoentity/domain.py	(revision 0fbb01a687097a66373b31056aaa65a85064b51a)
+++ flexoentity/domain.py	(revision e458b5a04c0ef82f3ff6446cbd483b09b52f3c67)
@@ -26,15 +26,11 @@
         return self.domain_id
 
-    def to_dict(self):
-        base = super().to_dict()
-        base.update({
-            "flexo_id": self.flexo_id,
-            "domain_id": self.domain_id,
+    def _serialize_content(self):
+        return {
             "fullname": self.fullname,
             "description": self.description,
             "classification": self.classification,
-        })
-        return base
-
+        }
+    
     @classmethod
     def from_dict(cls, data):
Index: flexoentity/flexo_signature.py
===================================================================
--- flexoentity/flexo_signature.py	(revision 0fbb01a687097a66373b31056aaa65a85064b51a)
+++ flexoentity/flexo_signature.py	(revision e458b5a04c0ef82f3ff6446cbd483b09b52f3c67)
@@ -73,4 +73,13 @@
     comment: Optional[str] = None
 
+    def _serialize_content(self):
+        return {
+            "signed_entity": self.signed_entity,
+            "signer_id": str(self.signer_id),
+            "signature_data": self.signature_data,
+            "certificate_reference": self.certificate_reference.to_dict(),
+            "certificate_thumbprint": self.certificate_thumbprint
+        }
+
     @property
     def text_seed(self):
Index: tests/conftest.py
===================================================================
--- tests/conftest.py	(revision 0fbb01a687097a66373b31056aaa65a85064b51a)
+++ tests/conftest.py	(revision e458b5a04c0ef82f3ff6446cbd483b09b52f3c67)
@@ -59,11 +59,9 @@
         return cls()
 
-    def to_dict(self):
-        base = super().to_dict()
-        base.update({
+    def _serialize_content(self):
+        return {
             "text": self.text,
             "options": [opt.to_dict() for opt in self.options],
-        })
-        return base
+        }
 
     @property