then probably you should go for "directory synchronization"
In short you need to maintain a machine which can sync details (objects i.e. User details) and put in File system which can be accessed by LDAP protocols on top of it and serve you the request even if your application is running offline !
Condition : At-least your app should be able to connected and talk local AD or Directory machine !
but before that you need peep in to these specs :
Quote:Review object limits
Review requirements for the directory synchronization computer
Review requirements for the domain controllers
Ensure you have administrator permissions
Review performance considerations
Review hardware recommendations
Review your Windows Azure AD authentication requirements
Follow this : LINK