Updated Description metadata to sentence case.

Author: ttorble

articles/cosmos-db/managed-identity-based-authentication.md

@@ -1,6 +1,6 @@
 ---
 title: How to use a system-assigned managed identity to access Azure Cosmos DB data
-description: Learn how to configure an Azure AD system-assigned managed identity to access keys from Azure Cosmos DB. msi, managed service identity, aad, azure active directory, identity
+description: Learn how to configure an Azure Active Directory (Azure AD) system-assigned managed identity (managed service identity) to access keys from Azure Cosmos DB. 
 author: j-patrick
 ms.service: cosmos-db
 ms.topic: conceptual