Add SDK Feature Flags (#313)

## Summary of the Pull Request

This enables feature flags for the SDK, which enables gating access to preview features to those that have specifically asked for them.  This is intended to be used within #266.

Note, this change also moves to using a `pydantic` model for the config, rather than hand-crafted JSON dicts.

src/cli/onefuzz/api.py

@@ -9,6 +9,7 @@ import os
 import re
 import subprocess  # nosec
 import uuid
+from enum import Enum
 from shutil import which
 from typing import Callable, Dict, List, Optional, Tuple, Type, TypeVar, cast
 from uuid import UUID
@@ -21,15 +22,15 @@ from pydantic import BaseModel
 from six.moves import input  # workaround for static analysis
 
 from .__version__ import __version__
-from .backend import Backend, ContainerWrapper, wait
+from .backend import Backend, BackendConfig, ContainerWrapper, wait
 from .ssh import build_ssh_command, ssh_connect, temp_file
 
 UUID_EXPANSION = TypeVar("UUID_EXPANSION", UUID, str)
 
-DEFAULT = {
-    "authority": "https://login.microsoftonline.com/72f988bf-86f1-41af-91ab-2d7cd011db47",
-    "client_id": "72f1562a-8c0c-41ea-beb9-fa2b71c80134",
-}
+DEFAULT = BackendConfig(
+    authority="https://login.microsoftonline.com/72f988bf-86f1-41af-91ab-2d7cd011db47",
+    client_id="72f1562a-8c0c-41ea-beb9-fa2b71c80134",
+)
 
 # This was generated randomly and should be preserved moving forwards
 ONEFUZZ_GUID_NAMESPACE = uuid.UUID("27f25e3f-6544-4b69-b309-9b096c5a9cbc")
@@ -44,6 +45,10 @@ REPRO_SSH_FORWARD = "1337:127.0.0.1:1337"
 UUID_RE = r"^[a-f0-9]{8}-?[a-f0-9]{4}-?[a-f0-9]{4}-?[a-f0-9]{4}-?[a-f0-9]{12}\Z"
 
 
+class PreviewFeature(Enum):
+    pass
+
+
 def is_uuid(value: str) -> bool:
     return bool(re.match(UUID_RE, value))
 
@@ -1449,7 +1454,7 @@ class Onefuzz:
 
     def __setup__(self, endpoint: Optional[str] = None) -> None:
         if endpoint:
-            self._backend.config["endpoint"] = endpoint
+            self._backend.config.endpoint = endpoint
 
     def licenses(self) -> object:
         """ Return third-party licenses used by this package """
@@ -1476,7 +1481,8 @@ class Onefuzz:
         authority: Optional[str] = None,
         client_id: Optional[str] = None,
         client_secret: Optional[str] = None,
-    ) -> Dict[str, str]:
+        enable_feature: Optional[PreviewFeature] = None,
+    ) -> BackendConfig:
         """ Configure onefuzz CLI """
         self.logger.debug("set config")
 
@@ -1493,22 +1499,24 @@ class Onefuzz:
                     "This could be an invalid OneFuzz API endpoint: "
                     "Missing HTTP Authentication"
                 )
-            self._backend.config["endpoint"] = endpoint
+            self._backend.config.endpoint = endpoint
         if authority is not None:
-            self._backend.config["authority"] = authority
+            self._backend.config.authority = authority
         if client_id is not None:
-            self._backend.config["client_id"] = client_id
+            self._backend.config.client_id = client_id
         if client_secret is not None:
-            self._backend.config["client_secret"] = client_secret
+            self._backend.config.client_secret = client_secret
+        if enable_feature:
+            self._backend.enable_feature(enable_feature.name)
         self._backend.app = None
         self._backend.save_config()
 
-        data: Dict[str, str] = self._backend.config.copy()
-        if "client_secret" in data:
+        data = self._backend.config.copy(deep=True)
+        if data.client_secret is not None:
             # replace existing secrets with "*** for user display
-            data["client_secret"] = "***"  # nosec
+            data.client_secret = "***"  # nosec
 
-        if not data["endpoint"]:
+        if not data.endpoint:
             self.logger.warning("endpoint not configured yet")
 
         return data
@@ -1655,6 +1663,12 @@ class Onefuzz:
             webhooks=webhooks,
         )
 
+    def _warn_preview(self, feature: PreviewFeature) -> None:
+        self.logger.warning(
+            "%s are a preview-feature and may change in an upcoming release",
+            feature.name,
+        )
+
 
 from .debug import Debug  # noqa: E402
 from .status.cmd import Status  # noqa: E402