diff --git a/swh/journal/serializers.py b/swh/journal/serializers.py
--- a/swh/journal/serializers.py
+++ b/swh/journal/serializers.py
@@ -12,9 +12,12 @@
 from swh.model.model import (
     Content,
     Directory,
+    MetadataAuthority,
+    MetadataFetcher,
     Origin,
     OriginVisit,
     OriginVisitStatus,
+    RawExtrinsicMetadata,
     Release,
     Revision,
     SkippedContent,
@@ -24,9 +27,12 @@
 ModelObject = Union[
     Content,
     Directory,
+    MetadataAuthority,
+    MetadataFetcher,
     Origin,
     OriginVisit,
     OriginVisitStatus,
+    RawExtrinsicMetadata,
     Release,
     Revision,
     SkippedContent,
@@ -54,7 +60,14 @@
 
 @overload
 def object_key(
-    object_type: str, object_: Union[OriginVisit, OriginVisitStatus]
+    object_type: str,
+    object_: Union[
+        MetadataAuthority,
+        MetadataFetcher,
+        OriginVisit,
+        OriginVisitStatus,
+        RawExtrinsicMetadata,
+    ],
 ) -> Dict[str, str]:
     ...
 
@@ -79,6 +92,26 @@
             "visit": str(object_.visit),
             "date": str(object_.date),
         }
+    elif object_type == "metadata_authority":
+        return {
+            "type": object_.type.value,
+            "url": object_.url,
+        }
+    elif object_type == "metadata_fetcher":
+        return {
+            "name": object_.name,
+            "version": object_.version,
+        }
+    elif object_type == "raw_extrinsic_metadata":
+        return {
+            "type": object_.type.value,
+            "id": str(object_.id),
+            "authority_type": object_.authority.type.value,
+            "authority_url": object_.authority.url,
+            "discovery_date": str(object_.discovery_date),
+            "fetcher_name": object_.fetcher.name,
+            "fetcher_version": object_.fetcher.version,
+        }
     else:
         raise ValueError("Unknown object type: %s." % object_type)
 
diff --git a/swh/journal/tests/journal_data.py b/swh/journal/tests/journal_data.py
--- a/swh/journal/tests/journal_data.py
+++ b/swh/journal/tests/journal_data.py
@@ -9,18 +9,24 @@
 
 import attr
 
-from swh.model.hashutil import MultiHash, hash_to_bytes
+from swh.model.hashutil import MultiHash, hash_to_bytes, hash_to_hex
 from swh.journal.serializers import ModelObject
 
+from swh.model.identifiers import SWHID
 from swh.model.model import (
     Content,
     Directory,
     DirectoryEntry,
+    MetadataAuthority,
+    MetadataAuthorityType,
+    MetadataFetcher,
+    MetadataTargetType,
     ObjectType,
     Origin,
     OriginVisit,
     OriginVisitStatus,
     Person,
+    RawExtrinsicMetadata,
     Release,
     Revision,
     RevisionType,
@@ -288,12 +294,47 @@
 ]
 
 
+METADATA_AUTHORITIES = [
+    MetadataAuthority(
+        type=MetadataAuthorityType.FORGE, url="http://example.org/", metadata={},
+    ),
+]
+
+METADATA_FETCHERS = [
+    MetadataFetcher(name="test-fetcher", version="1.0.0", metadata={},)
+]
+
+RAW_EXTRINSIC_METADATA = [
+    RawExtrinsicMetadata(
+        type=MetadataTargetType.ORIGIN,
+        id="http://example.org/foo.git",
+        discovery_date=datetime.datetime(2020, 7, 30, 17, 8, 20, tzinfo=UTC),
+        authority=attr.evolve(METADATA_AUTHORITIES[0], metadata=None),
+        fetcher=attr.evolve(METADATA_FETCHERS[0], metadata=None),
+        format="json",
+        metadata=b'{"foo": "bar"}',
+    ),
+    RawExtrinsicMetadata(
+        type=MetadataTargetType.CONTENT,
+        id=SWHID(object_type="content", object_id=hash_to_hex(CONTENTS[0].sha1_git)),
+        discovery_date=datetime.datetime(2020, 7, 30, 17, 8, 20, tzinfo=UTC),
+        authority=attr.evolve(METADATA_AUTHORITIES[0], metadata=None),
+        fetcher=attr.evolve(METADATA_FETCHERS[0], metadata=None),
+        format="json",
+        metadata=b'{"foo": "bar"}',
+    ),
+]
+
+
 TEST_OBJECTS: Dict[str, Sequence[ModelObject]] = {
     "content": CONTENTS,
     "directory": DIRECTORIES,
+    "metadata_authority": METADATA_AUTHORITIES,
+    "metadata_fetcher": METADATA_FETCHERS,
     "origin": ORIGINS,
     "origin_visit": ORIGIN_VISITS,
     "origin_visit_status": ORIGIN_VISIT_STATUSES,
+    "raw_extrinsic_metadata": RAW_EXTRINSIC_METADATA,
     "release": RELEASES,
     "revision": REVISIONS,
     "snapshot": SNAPSHOTS,
diff --git a/swh/journal/tests/test_pytest_plugin.py b/swh/journal/tests/test_pytest_plugin.py
--- a/swh/journal/tests/test_pytest_plugin.py
+++ b/swh/journal/tests/test_pytest_plugin.py
@@ -54,9 +54,12 @@
         "object_types": {
             "content",
             "directory",
+            "metadata_authority",
+            "metadata_fetcher",
             "origin",
             "origin_visit",
             "origin_visit_status",
+            "raw_extrinsic_metadata",
             "release",
             "revision",
             "snapshot",