Azure AD App registrations provides ways for authenticating
or authorizing the user custom applications which uses Azure AD, to access the
data available on the Microsoft products/services.
Why Azure AD App Registration? You might have already worked
with custom applications that uses Azure Control Service, which provides way
for authenticating users to gain access to web applications and services. As
ACS is getting deprecated, Microsoft provides ways for authenticating the
applications and provides way for enabling permissions for users to access the
data.
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| (Source: https://cloudblogs.microsoft.com/enterprisemobility/2013/06/22/azure-active-directory-is-the-future-of-acs/) |
