Build a basic android REST Client

I need an android REST client, built on Java using [login to view URL] There shouldn't be any other dependency. Requirements & Details 1. The API server uses OAuth2, the client should authenticate with the API with the implicit grant. Few points on this. a) You shouldn't use the web view to accomplish this. b) The opened browser tab should be closed after the authentication is finished. 2. Authentication should happen securely a) The implicit grant from the server supports CSRF validation, that should be implemented. b) Other security practices should be implemented. 3. The tokens should be stored securely. (On the bid, please mention where you are going to store the tokens and how you are going to make it secure) 4. Simple RBAC, when logged in as admin, can create users (also through the API). Point to note: a) The user has a 1 to 1 relation with an Entity called `contact` 5. Implement CRUD functionality for only ONE entity offered in the API. 4. The code should be properly structured into tiers. 5. Proper naming convention 6. Proper documentation of code, method and classes 7. Unit testing 8. Proper logs to assist in debug 9. Build instructions 10. Setup instructions 11. Packaged work Final notes: - ER Diagram, Details on the API and sections will be given privately to the shortlisted candidate. - I want to hear your questions. - To should be able to demonstrate your experience with OAuth2 & Retrofit. Happy bidding!