Package 'AppForSharePoint16WebToolkit.4.0.0' is not found on source 'https://api.nuget.org/v3/index.json'.

For some reason, when we create a new sharepoint provider hosted app in visual studio it adds a reference to the package 'AppForSharePoint16WebToolkit.4.0.0'. This package is no longer available on nuget and the latest stable version is 'AppForSharePoint16WebToolkit.3.1.5'. So to rectify this error we need to uninstall this package and reinstall the available version which is fairly straightforward.

However, when we compile the solution after replacing the package, we get another error that 'SecurityTokenException' class is not available (in SharePointContext.cs file). This error can be easily fixed by replacing 'SecurityTokenException' with 'SecurityTokenExpiredException'