In my Azure Function I am using a Library which establishes a connection to an SQL server via the ConnectionString from the ConfigurationManager like this:
v
// C# Environment Variables example for Azure Functions v1 or v2 runtime
// This works all the way up to but not including .NET Core 2.0
var clientId = Environment.GetEnvironmentVariable("ClientId");
var clientSecret = Environment.GetEnvironmentVariable("ClientSecret");
var aadDomain = Environment.GetEnvironmentVariable("AADDomain");
Please do remember the settings you do in local.settings.json will not be reflected in azure. Please add your values in app setting from Azure portal follow the link- https://docs.microsoft.com/en-us/azure/azure-functions/functions-how-to-use-azure-function-app-settings