This is a very simple example of using OAuth antentication for developing SAS applications; I stress the "simple" since there is no other advantage over the ReactJS application example in which this project is based on.
On top of not using Reactjs (just to focus on the bare minimum) there is another difference: the goal of this app, currently, is to obtain a token using existing credentials, and fail if they don't exist. This means that there is no logic for opening up the SASLogon popup, and also no use of a callback function.