code: public DropboxClient authenticate(String email, String password) {
          OAuthRequest request = new OAuthRequest(Verb.GET, DropboxApi.MOBILE_AUTH_URL);
          request.addQuerystringParameter("email", email);
          request.addQuerystringParameter("password", password);
          service.signRequest(requestToken, request);
  
          accessToken = Json.parse(request.send().getBody(), DropboxAccessToken.class).toOauthToken();
  
          return buildDropboxClient();
      }
docs: --- MobileAuthentication Impl ---