Updated: Mar 29, 2019
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.
The following method is one way for registering the custom built applications and authenticating users for accessing Microsoft services.
Azure AD has options for registering the user custom applications, where users can provide the app details like app name, application type (web or native app) and sign-on page URL. This helps authenticating users for accessing the application data.
Then navigate to the required permissions option. Select the required API and add the necessary permissions and save it. After saving, click on grant permissions for enabling users to access the data.