Application settings contain the Azure Storage Account Connection string. The function app is designed to generate the SAS token. Have set the Azure Storage Account connection string as part of the Application settings to the function app. When the application is hosted on Azure it returns undefined.
However, the same connection string which is stored in local.settings.json is able to read when running locally.
Bellow is the code to read the connection string in Azure Function
let connectionString = process.env.AZURE_STORAGE_CONNECTION_STRING;
context.log("context - Connection String ", connectionString);
This returns the correct connection string when running locally but not when published to server.
Local.Settings.json code

Function app Application Settings




