I have to design an external app which will retrieve information from Salesforce. Any user can install this app and use it. This app will use rest API to access information from Salesforce. I cannot force the users belonging to multiple orgs to create a connected app in their instance to generate consumer key and consumer secret. Ideally users must be able to enter username and password+security token to access the data. Is there a way to achieve this or any other way without much customization by the admin.