Clear app data and maintain logins As the title says, is there a way to clear all the data of a specific app leaving untouched it's login, settings and other personal information ?

There are tons of garbage files that a cache cleaning won't clean.
Android system clears all the app's private data when clear data is selected. Since all the app specific data(preferences, database,cache) stored in app's specific folder, everything will be deleted. if you still wanted to maintain that data, you can store the login information in either server/some other location on the device.