diff --git a/addon_service/addon_operation/models.py b/addon_service/addon_operation/models.py
index 7e906465..9fd279c8 100644
--- a/addon_service/addon_operation/models.py
+++ b/addon_service/addon_operation/models.py
@@ -7,14 +7,17 @@
     get_imp_name,
 )
 from addon_service.common.static_dataclass_model import StaticDataclassModel
-from addon_toolkit import AddonOperationImp
+from addon_toolkit import (
+    AddonCapabilities,
+    AddonOperationImp,
+)
 from addon_toolkit.json_arguments import jsonschema_for_signature_params
 from addon_toolkit.operation import AddonOperationType
 
 
 # dataclass wrapper for addon_toolkit.AddonOperationImp that sufficiently
 # meets rest_framework_json_api expectations on a model class
-@dataclasses.dataclass(frozen=True, kw_only=True)
+@dataclasses.dataclass(frozen=True)
 class AddonOperationModel(StaticDataclassModel):
     operation_imp: AddonOperationImp
 
@@ -42,7 +45,7 @@ def implementation_docstring(self) -> str:
         return self.operation_imp.imp_function.__doc__ or ""
 
     @cached_property
-    def capability(self) -> str:
+    def capability(self) -> AddonCapabilities:
         return self.operation_imp.declaration.capability
 
     @cached_property
diff --git a/addon_service/addon_operation/serializers.py b/addon_service/addon_operation/serializers.py
index 875b1f47..fcc39981 100644
--- a/addon_service/addon_operation/serializers.py
+++ b/addon_service/addon_operation/serializers.py
@@ -1,11 +1,11 @@
 from rest_framework_json_api import serializers
 from rest_framework_json_api.utils import get_resource_type_from_model
 
-from addon_service.addon_imp.models import AddonImp
 from addon_service.common import view_names
 from addon_service.common.enums.serializers import EnumNameChoiceField
 from addon_service.common.serializer_fields import DataclassRelatedDataField
 from addon_toolkit import AddonCapabilities
+from addon_toolkit.imp import AddonImp
 
 from .models import AddonOperationModel
 
diff --git a/addon_service/authorized_storage_account/models.py b/addon_service/authorized_storage_account/models.py
index 647db7a3..ee2578c8 100644
--- a/addon_service/authorized_storage_account/models.py
+++ b/addon_service/authorized_storage_account/models.py
@@ -121,7 +121,7 @@ def authorized_operation_names(self):
         ]
 
     @property
-    def auth_url(self) -> str:
+    def auth_url(self) -> str | None:
         """Generates the url required to initiate OAuth2 credentials exchange.
 
         Returns None if the ExternalStorageService does not support OAuth2
diff --git a/addon_toolkit/operation.py b/addon_toolkit/operation.py
index 75efe879..787d00b5 100644
--- a/addon_toolkit/operation.py
+++ b/addon_toolkit/operation.py
@@ -7,6 +7,7 @@
     Iterator,
 )
 
+from .capabilities import AddonCapabilities
 from .declarator import Declarator
 
 
@@ -35,7 +36,7 @@ class AddonOperationDeclaration:
     """
 
     operation_type: AddonOperationType
-    capability: enum.Enum
+    capability: AddonCapabilities
     operation_fn: Callable  # the decorated function
     return_type: type = dataclasses.field(
         default=type(None),  # if not provided, inferred by __post_init__
@@ -99,7 +100,13 @@ def param_dataclasses(self) -> Iterator[type]:
 @dataclasses.dataclass
 class RedirectResult:
     url: str
-    method: HTTPMethod = HTTPMethod.GET
+    method: str = HTTPMethod.GET
+
+    def __post_init__(self):
+        try:
+            HTTPMethod(self.method)
+        except ValueError:
+            raise ValueError(f'invalid http method "{self.method}"')
 
 
 # decorator for operations that may be performed by a client request (e.g. redirect to waterbutler)
diff --git a/addon_toolkit/tests/test_addon_protocol.py b/addon_toolkit/tests/test_addon_protocol.py
index f3cf470c..267bdaca 100644
--- a/addon_toolkit/tests/test_addon_protocol.py
+++ b/addon_toolkit/tests/test_addon_protocol.py
@@ -25,7 +25,7 @@ class _MyCapability(enum.Enum):
         UNUSED = "unused"  # for testing when a capability has no operations
 
     ###
-    # shared test env (on `self`)
+    # shared test env (initialized by setUpClass)
     _MyProtocol: type  # typing.Protocol subclass decorated with `@addon_protocol`
     _MyImplementation: type  # subclass of _MyProtocol
     _my_imp: AddonImp