Inherit upstream Attestation to keep Sigstore path

Author: jobselko

pulp_python/app/provenance.py

@@ -10,13 +10,8 @@
 from django.conf import settings
 from pydantic import BaseModel, ConfigDict, Field
 from pydantic.alias_generators import to_snake
-from pypi_attestations import (
-    Distribution,
-    Envelope,
-    Publisher,
-    VerificationError,
-    VerificationMaterial,
-)
+from pypi_attestations import Attestation as _UpstreamAttestation
+from pypi_attestations import Distribution, Publisher, VerificationError, VerificationMaterial
 from sigstore.dsse import Envelope as DSSEEnvelope
 from sigstore.dsse import _pae
 
@@ -57,24 +52,20 @@ def _as_policy(self):
 ExtendedPublisher = Annotated[_ExtendedPublisherUnion, Field(union_mode="left_to_right")]
 
 
-class Attestation(BaseModel):
-    """Attestation object as defined in PEP 740."""
-
-    version: Literal[1]
+class Attestation(_UpstreamAttestation):
     """
-    The attestation format's version, which is always 1.
+    Attestation object as defined in PEP 740.
+
+    Inherits from the upstream pypi_attestations.Attestation to keep Sigstore
+    verification methods (to_bundle, verify), but makes verification_material
+    optional to support attestations signed with a custom key instead of Sigstore.
     """
 
     verification_material: VerificationMaterial | None = None
     """
     Cryptographic materials used to verify `message_signature`.
     """
 
-    envelope: Envelope
-    """
-    The enveloped attestation statement and signature.
-    """
-
 
 class AttestationBundle(BaseModel):
     """