To answer your query "Does app42 store the logged in user locally itself", yes once you call authenticate object we save logged in user and session id local pref. And you get logged in user value using getLoggedInUser function.
let me know if it helps.
P.S We also support saving user additional information in Storage service where you can store any value in JSON format. Please have a look at this link and let me know if you require any help.