fix: allow signed post policy v4 with service account and token (#1356)

google/cloud/storage/client.py

@@ -1724,13 +1724,16 @@ def generate_signed_post_policy_v4(
             )
 
         credentials = self._credentials if credentials is None else credentials
-        ensure_signed_credentials(credentials)
+        client_email = service_account_email
+        if not access_token or not service_account_email:
+            ensure_signed_credentials(credentials)
+            client_email = credentials.signer_email
 
         # prepare policy conditions and fields
         timestamp, datestamp = get_v4_now_dtstamps()
 
         x_goog_credential = "{email}/{datestamp}/auto/storage/goog4_request".format(
-            email=credentials.signer_email, datestamp=datestamp
+            email=client_email, datestamp=datestamp
         )
         required_conditions = [
             {"bucket": bucket_name},

tests/system/test__signing.py

@@ -415,6 +415,55 @@ def test_generate_signed_post_policy_v4(
     assert blob.download_as_bytes() == payload
 
 
+@pytest.mark.skipif(
+    _helpers.is_api_endpoint_override,
+    reason="Test does not yet support endpoint override",
+)
+def test_generate_signed_post_policy_v4_access_token_sa_email(
+    storage_client, signing_bucket, blobs_to_delete, service_account, no_mtls
+):
+    client = iam_credentials_v1.IAMCredentialsClient()
+    service_account_email = service_account.service_account_email
+    name = path_template.expand(
+        "projects/{project}/serviceAccounts/{service_account}",
+        project="-",
+        service_account=service_account_email,
+    )
+    scope = [
+        "https://www.googleapis.com/auth/devstorage.read_write",
+        "https://www.googleapis.com/auth/iam",
+    ]
+    response = client.generate_access_token(name=name, scope=scope)
+
+    now = _NOW(_UTC).replace(tzinfo=None)
+    blob_name = "post_policy_obj_email2.txt"
+    payload = b"DEADBEEF"
+    with open(blob_name, "wb") as f:
+        f.write(payload)
+    policy = storage_client.generate_signed_post_policy_v4(
+        signing_bucket.name,
+        blob_name,
+        conditions=[
+            {"bucket": signing_bucket.name},
+            ["starts-with", "$Content-Type", "text/pla"],
+        ],
+        expiration=now + datetime.timedelta(hours=1),
+        fields={"content-type": "text/plain"},
+        service_account_email=service_account_email,
+        access_token=response.access_token,
+    )
+    with open(blob_name, "r") as f:
+        files = {"file": (blob_name, f)}
+        response = requests.post(policy["url"], data=policy["fields"], files=files)
+
+    os.remove(blob_name)
+    assert response.status_code == 204
+
+    blob = signing_bucket.get_blob(blob_name)
+    blobs_to_delete.append(blob)
+    assert blob.download_as_bytes() == payload
+
+
 def test_generate_signed_post_policy_v4_invalid_field(
     storage_client, buckets_to_delete, blobs_to_delete, service_account, no_mtls
 ):

tests/unit/test_client.py

@@ -2849,6 +2849,50 @@ def test_get_signed_policy_v4_with_access_token(self):
         self.assertEqual(fields["x-goog-signature"], EXPECTED_SIGN)
         self.assertEqual(fields["policy"], EXPECTED_POLICY)
 
+    def test_get_signed_policy_v4_with_access_token_sa_email(self):
+        import datetime
+
+        BUCKET_NAME = "bucket-name"
+        BLOB_NAME = "object-name"
+        EXPECTED_SIGN = "0c4003044105"
+        EXPECTED_POLICY = "eyJjb25kaXRpb25zIjpbeyJidWNrZXQiOiJidWNrZXQtbmFtZSJ9LHsiYWNsIjoicHJpdmF0ZSJ9LFsic3RhcnRzLXdpdGgiLCIkQ29udGVudC1UeXBlIiwidGV4dC9wbGFpbiJdLHsiYnVja2V0IjoiYnVja2V0LW5hbWUifSx7ImtleSI6Im9iamVjdC1uYW1lIn0seyJ4LWdvb2ctZGF0ZSI6IjIwMjAwMzEyVDExNDcxNloifSx7IngtZ29vZy1jcmVkZW50aWFsIjoidGVzdEBtYWlsLmNvbS8yMDIwMDMxMi9hdXRvL3N0b3JhZ2UvZ29vZzRfcmVxdWVzdCJ9LHsieC1nb29nLWFsZ29yaXRobSI6IkdPT0c0LVJTQS1TSEEyNTYifV0sImV4cGlyYXRpb24iOiIyMDIwLTAzLTI2VDAwOjAwOjEwWiJ9"
+
+        project = "PROJECT"
+        credentials = _make_credentials(project=project)
+        client = self._make_one(credentials=credentials)
+
+        dtstamps_patch, now_patch, expire_secs_patch = _time_functions_patches()
+        with dtstamps_patch, now_patch, expire_secs_patch:
+            with mock.patch(
+                "google.cloud.storage.client._sign_message", return_value=b"DEADBEEF"
+            ):
+                policy = client.generate_signed_post_policy_v4(
+                    BUCKET_NAME,
+                    BLOB_NAME,
+                    expiration=datetime.datetime(2020, 3, 12),
+                    conditions=[
+                        {"bucket": BUCKET_NAME},
+                        {"acl": "private"},
+                        ["starts-with", "$Content-Type", "text/plain"],
+                    ],
+                    service_account_email="[email protected]",
+                    access_token="token",
+                )
+        self.assertEqual(
+            policy["url"], "https://storage.googleapis.com/" + BUCKET_NAME + "/"
+        )
+        fields = policy["fields"]
+
+        self.assertEqual(fields["key"], BLOB_NAME)
+        self.assertEqual(fields["x-goog-algorithm"], "GOOG4-RSA-SHA256")
+        self.assertEqual(fields["x-goog-date"], "20200312T114716Z")
+        self.assertEqual(
+            fields["x-goog-credential"],
+            "[email protected]/20200312/auto/storage/goog4_request",
+        )
+        self.assertEqual(fields["x-goog-signature"], EXPECTED_SIGN)
+        self.assertEqual(fields["policy"], EXPECTED_POLICY)
+
 
 class Test__item_to_bucket(unittest.TestCase):
     def _call_fut(self, iterator, item):