Most of the enterprise Web services you'll access are going to be secured - meaning they'll require you to pass a user/password in order to get to their data. 

If you never created a secured Web service, it's simple in JDeveloper! For the below video I just right clicked on a Java class that I exposed as a Web service, and chose  "Web Service Properties" and then checked the "oracle/wss_username_token_service_policy" box from the list of options (that's the option supported by ADF Mobile right now):

In the demo below we are going to use a "remote" login server that does the authentication of the user/pass.

The easiest way to "create" a remote login server is to create a "regular" web ADF application, secure it, and deploy it on a server. The secured ADF application can just require ADF Authentication with a simple HTTP Basic Authentication - basically the next two images in the Application->Secure->Configure ADF Security menu wizard.

ok - so now you have a secured ADF application - deploy it on a server and get the URL for that application. 

From this point on you'll see the process in the video which deals with the configuration of your ADF Mobile app.

First you'll need to enable security for your ADF mobile application, so it will prompt users to provide a user/pass combination.

You'll also need to configure security on specific features. And you can have them use remote login pointing to your regular secured ADF application.

Next define your Web service data control. Right click on the web service data control to "define Web Service Security".

You'll also need to define the adfCredentialStoreKey property for the Web Service data control in the connections.xml file.

This should be it. Here is the flow:

If you haven't already - you can read more about this in the Mobile developer guide, and Andrejus has a sample for you.