Azure Active Directory (Azure AD) is a cloud based, multitenant, and highly available identity management service from Microsoft:

We can manage users, groups, multifactor authentication, add an application that an organization is developing for authentication, add an application from the gallery for authentication, add a custom domain, role based access control, and so on:

Application Gallery supports more than 2500 applications at the time of writing this chapter:

The categories include business management, collaboration, construction, content management, CRM, data services, developer services, e-commerce, education, ERP, finance, health, human resources, IT infrastructure, mail, marketing, media, mobile device management, productivity, project management, security, social, supply management, telecommunications, travel, and web design and hosting.