How can I implement iOS TouchScreenKeyboard 'Next' and 'Go' keys?

It is very common to need to provide a login UI that follows this model...

Username: TextInputField Password: PasswordField Login_Button

On iOS, when the user touches the Username TextInputField, the virtual keyboard is displayed with a 'Next' key so that when the user is finished entering their username, they can touch the 'Next' key and put the focus on the PasswordField, which will cause a new virtual keyboard to be displayed with a "Go" or a "Submit" or (in the above example) a "Login" key so that when the user is finished entering their password, they can touch the "Login" key to dismiss the keyboard and execute the login method.

I've been looking for a way to accomplish this and have come up empty. Certainly some other Unity developers need this functionality as well. How are they solving this? Any help/suggestions will be greatly appreciated.