Stevie Graham did that in Teller (http://teller.io/), i.e. he reverse engineered the mobile apps (https://news.ycombinator.com/item?id=11077362). But I think that controlling a browser programmatically and scraping pages is an easier approach. Sometimes it may even be the only possible one (ex. if encryption is used at the app level).
«Boobank is a console application able to list your bank accounts balances on supported websites and to see the expenses details, transfer money, etc.»
Another approach to consider would be reverse engineering the mobile apps to gain access to the private API.
Also, be careful not to commit any files with your username and password in them while testing! :O