In the current Microsoft cloud world, there are two core identity management systems – 1) the Microsoft account and 2) the Azure AD account. As a user, you are continually asked to choose whether you are a business user or a personal user and then you login using one of these two paths.
For developers building applications against these identity stores, there are two separate APIs to contend with to authenticate the user, enforcing the same forking of the authentication workflow and making it more complex to build applications.
Microsoft has announced that they are working on a consolidated authentication flow and API that will provide a consolidated user experience and API for developers. The App Model v2.0 is now in preview.
Instead of forcing the user to tell us what type of account they are using, the API will figure it out under the covers and authenticate using either account type in a single flow. In addition, the API for authenticate either Microsoft personal accounts or AD Azure accounts will be the same to make it easier for developers to build external applications that use these accounts as identities.