Add connection string auth to cosmos (#3867)

Adds a connection string option for the cosmos memory, in case AAD auth
is not enabled on the cosmos instance.

langchain/memory/chat_message_histories/cosmos_db.py

@@ -28,26 +28,34 @@ class CosmosDBChatMessageHistory(BaseChatMessageHistory):
         cosmos_endpoint: str,
         cosmos_database: str,
         cosmos_container: str,
-        credential: Any,
         session_id: str,
         user_id: str,
+        credential: Any = None,
+        connection_string: Optional[str] = None,
         ttl: Optional[int] = None,
     ):
         """
         Initializes a new instance of the CosmosDBChatMessageHistory class.
 
+        Make sure to call prepare_cosmos or use the context manager to make
+        sure your database is ready.
+
+        Either a credential or a connection string must be provided.
+
         :param cosmos_endpoint: The connection endpoint for the Azure Cosmos DB account.
         :param cosmos_database: The name of the database to use.
         :param cosmos_container: The name of the container to use.
-        :param credential: The credential to use to authenticate to Azure Cosmos DB.
         :param session_id: The session ID to use, can be overwritten while loading.
         :param user_id: The user ID to use, can be overwritten while loading.
+        :param credential: The credential to use to authenticate to Azure Cosmos DB.
+        :param connection_string: The connection string to use to authenticate.
         :param ttl: The time to live (in seconds) to use for documents in the container.
         """
         self.cosmos_endpoint = cosmos_endpoint
         self.cosmos_database = cosmos_database
         self.cosmos_container = cosmos_container
         self.credential = credential
+        self.conn_string = connection_string
         self.session_id = session_id
         self.user_id = user_id
         self.ttl = ttl
@@ -70,9 +78,16 @@ class CosmosDBChatMessageHistory(BaseChatMessageHistory):
             raise ImportError(
                 "You must install the azure-cosmos package to use the CosmosDBChatMessageHistory."  # noqa: E501
             ) from exc
-        self._client = CosmosClient(
-            url=self.cosmos_endpoint, credential=self.credential
-        )
+        if self.credential:
+            self._client = CosmosClient(
+                url=self.cosmos_endpoint, credential=self.credential
+            )
+        elif self.conn_string:
+            self._client = CosmosClient.from_connection_string(
+                conn_str=self.conn_string
+            )
+        else:
+            raise ValueError("Either a connection string or a credential must be set.")
         database = self._client.create_database_if_not_exists(self.cosmos_database)
         self._container = database.create_container_if_not_exists(
             self.cosmos_container,