microsoft · axelsrz · Apr 15, 2021 · Apr 15, 2021 · Apr 15, 2021 · Apr 15, 2021
diff --git a/libraries/botbuilder-core/botbuilder/core/bot_framework_adapter.py b/libraries/botbuilder-core/botbuilder/core/bot_framework_adapter.py
@@ -512,7 +512,9 @@ async def process_activity_with_identity(
                 return InvokeResponse(status=int(HTTPStatus.NOT_IMPLEMENTED))
             return InvokeResponse(
                 status=invoke_response.value.status,
-                body=invoke_response.value.body.serialize(),
+                body=invoke_response.value.body.serialize()
+                if invoke_response.value.body
+                else None,
             )
 
         return None
@@ -1278,7 +1280,7 @@ async def exchange_token_from_credentials(
                 token=result.token,
                 expiration=result.expiration,
             )
-        raise TypeError(f"exchange_async returned improper result: {type(result)}")
+        raise TypeError(f"exchange token returned improper result: {type(result)}")
 
     @staticmethod
     def key_for_connector_client(service_url: str, app_id: str, scope: str):

diff --git a/libraries/botbuilder-core/botbuilder/core/memory_storage.py b/libraries/botbuilder-core/botbuilder/core/memory_storage.py
@@ -67,7 +67,7 @@ async def write(self, changes: Dict[str, StoreItem]):
                     old_state_etag is not None
                     and new_value_etag is not None
                     and new_value_etag != "*"
-                    and new_value_etag < old_state_etag
+                    and new_value_etag != old_state_etag
                 ):
                     raise KeyError(
                         "Etag conflict.\nOriginal: %s\r\nCurrent: %s"

diff --git a/libraries/botbuilder-core/botbuilder/core/teams/__init__.py b/libraries/botbuilder-core/botbuilder/core/teams/__init__.py
@@ -12,10 +12,12 @@
     teams_get_team_info,
     teams_notify_user,
 )
+from .teams_sso_token_exchange_middleware import TeamsSSOTokenExchangeMiddleware
 
 __all__ = [
     "TeamsActivityHandler",
     "TeamsInfo",
+    "TeamsSSOTokenExchangeMiddleware",
     "teams_get_channel_id",
     "teams_get_team_info",
     "teams_notify_user",

diff --git a/libraries/botbuilder-core/botbuilder/core/teams/teams_sso_token_exchange_middleware.py b/libraries/botbuilder-core/botbuilder/core/teams/teams_sso_token_exchange_middleware.py
@@ -0,0 +1,189 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+import traceback
+
+from http import HTTPStatus
+from typing import Awaitable, Callable
+from botframework.connector.channels import Channels
+
+from botframework.connector.token_api.models import (
+    TokenResponse,
+    TokenExchangeRequest,
+)
+from botbuilder.schema import (
+    Activity,
+    ActivityTypes,
+    SignInConstants,
+    TokenExchangeInvokeRequest,
+    TokenExchangeInvokeResponse,
+)
+from botbuilder.core import (
+    ExtendedUserTokenProvider,
+    Middleware,
+    InvokeResponse,
+    Storage,
+    StoreItem,
+    TurnContext,
+)
+
+
+class _TokenStoreItem(StoreItem):
+    def __init__(self, **kwargs):
+        self.e_tag: str = None
+        super().__init__(**kwargs)
+
+    @staticmethod
+    def get_storage_key(turn_context: TurnContext):
+        activity = turn_context.activity
+        if not activity.channel_id:
+            raise TypeError("invalid activity-missing channel_id")
+
+        if not activity.conversation or not activity.conversation.id:
+            raise TypeError("invalid activity-missing conversation.id")
+
+        channel_id = activity.channel_id
+        conversation_id = activity.conversation.id
+
+        value = activity.value
+        if not value or "id" not in value:
+            raise Exception("Invalid signin/tokenExchange. Missing activity.value[id]")
+
+        return f"{channel_id}/{conversation_id}/{value['id']}"
+
+
+class TeamsSSOTokenExchangeMiddleware(Middleware):
+    """
+    If the activity name is signin/tokenExchange, self middleware will attempt to
+    exchange the token, and deduplicate the incoming call, ensuring only one
+    exchange request is processed.
+
+    .. remarks::
+        If a user is signed into multiple Teams clients, the Bot could receive a
+        "signin/tokenExchange" from each client. Each token exchange request for a
+        specific user login will have an identical Activity.Value.Id.
+
+        Only one of these token exchange requests should be processed by the bot.
+        The others return <see cref="System.Net.HttpStatusCode.PreconditionFailed"/>.
+        For a distributed bot in production, self requires a distributed storage
+        ensuring only one token exchange is processed. self middleware supports
+        CosmosDb storage found in Microsoft.Bot.Builder.Azure, or MemoryStorage for
+        local development. IStorage's ETag implementation for token exchange activity
+        deduplication.
+    """
+
+    def __init__(self, storage: Storage, connection_name: str):
+        """
+        Initializes a instance of the <see cref="TeamsSSOTokenExchangeMiddleware"/> class.
+
+        :param storage: The Storage to use for deduplication.
+        :param connection_name: The connection name to use for the single
+        sign on token exchange.
+        """
+        if storage is None:
+            raise TypeError("storage cannot be None")
+
+        if connection_name is None:
+            raise TypeError("connection name cannot be None")
+
+        self._oauth_connection_name = connection_name
+        self._storage = storage
+
+    async def on_turn(
+        self, context: TurnContext, logic: Callable[[TurnContext], Awaitable]
+    ):
+        if (
+            context.activity.channel_id == Channels.ms_teams
+            and context.activity.name == SignInConstants.token_exchange_operation_name
+        ):
+            # If the TokenExchange is NOT successful, the response will have already been sent by _exchanged_token
+            if not await self._exchanged_token(context):
+                return
+
+            # Only one token exchange should proceed from here. Deduplication is performed second because in the case
+            # of failure due to consent required, every caller needs to receive the
+            if not await self._deduplicated_token_exchange_id(context):
+                # If the token is not exchangeable, do not process this activity further.
+                return
+
+        await logic()
+
+    async def _deduplicated_token_exchange_id(self, turn_context: TurnContext) -> bool:
+        # Create a StoreItem with Etag of the unique 'signin/tokenExchange' request
+        store_item = _TokenStoreItem(e_tag=turn_context.activity.value.get("id", None))
+
+        store_items = {_TokenStoreItem.get_storage_key(turn_context): store_item}
+        try:
+            # Writing the IStoreItem with ETag of unique id will succeed only once
+            await self._storage.write(store_items)
+        except Exception as error:
+            # Memory storage throws a generic exception with a Message of 'Etag conflict. [other error info]'
+            # CosmosDbPartitionedStorage throws: ex.Message.Contains("precondition is not met")
+            if "Etag conflict" in str(error) or "precondition is not met" in str(error):
+                # Do NOT proceed processing self message, some other thread or machine already has processed it.
+
+                # Send 200 invoke response.
+                await self._send_invoke_response(turn_context)
+                return False
+
+            raise error
+
+        return True
+
+    async def _send_invoke_response(
+        self,
+        turn_context: TurnContext,
+        body: object = None,
+        http_status_code=HTTPStatus.OK,
+    ):
+        await turn_context.send_activity(
+            Activity(
+                type=ActivityTypes.invoke_response,
+                value=InvokeResponse(status=http_status_code, body=body),
+            )
+        )
+
+    async def _exchanged_token(self, turn_context: TurnContext) -> bool:
+        token_exchange_response: TokenResponse = None
+        aux_dict = {}
+        if turn_context.activity.value:
+            for prop in ["id", "connection_name", "token", "properties"]:
+                aux_dict[prop] = turn_context.activity.value.get(prop)
+        token_exchange_request = TokenExchangeInvokeRequest(
+            id=aux_dict["id"],
+            connection_name=aux_dict["connection_name"],
+            token=aux_dict["token"],
+            properties=aux_dict["properties"],
+        )
+        try:
+            adapter = turn_context.adapter
+            if isinstance(turn_context.adapter, ExtendedUserTokenProvider):
+                token_exchange_response = await adapter.exchange_token(
+                    turn_context,
+                    self._oauth_connection_name,
+                    turn_context.activity.from_property.id,
+                    TokenExchangeRequest(token=token_exchange_request.token),
+                )
+            else:
+                raise Exception(
+                    "Not supported: Token Exchange is not supported by the current adapter."
+                )
+        except:
+            traceback.print_exc()
+        if not token_exchange_response or not token_exchange_response.token:
+            # The token could not be exchanged (which could be due to a consent requirement)
+            # Notify the sender that PreconditionFailed so they can respond accordingly.
+
+            invoke_response = TokenExchangeInvokeResponse(
+                id=token_exchange_request.id,
+                connection_name=self._oauth_connection_name,
+                failure_detail="The bot is unable to exchange token. Proceed with regular login.",
+            )
+
+            await self._send_invoke_response(
+                turn_context, invoke_response, HTTPStatus.PRECONDITION_FAILED
+            )
+
+            return False
+
+        return True