There is now support within iOS 7 for enterprise single sign-on. But it is another feature that means developers will need to rewrite their apps if they want to take advantage of it.
Apps that hook into this API will all be able to use the same authentication information, requiring the user to log in only once to access all the apps and corporate resources. This will, of course, require back-end support as well. Nevertheless, although certain apps and MDM systems already support single-sign on, having native support and a single system-wide API should make it easier for both MDM developers and app developers to ensure much greater compatibility, as well as support single sign-on in environments without MDM.