There doesn't appear to be much information available on developing a custom Azure Active Directory Enterprise Application. Is the developer information available anywhere?
e.g. develop an application that will appear in the list of Enterprise Applications in the Azure Active Directory gallery and that, once developed (in C#), allows SSO and provisioning of an external system, based on users and groups in Azure Active Directory
If you want to publish your app to azure ad gallery, you submit your request for access in the Application Network portal and implement SSO by using the federation protocol or by using the password SSO and request for user provisioning.
For more details of these steps, you can refer to this tutorial about how to publish the app to azure ad gallery. In this tutorial, there are also some links which may help you on how to do the development(such as integrate your application with Azure AD by using the Open ID Connect protocol, how to support SAML 2.0 and so on).
