Azure Active Directory B2C (Azure AD B2C, Azure Active Directory External Identities) is a customer identity access management (CIAM) solution capable of supporting millions of users and billions of authentications per day. It takes care of the scaling and safety of the authentication platform, monitoring, and automatically handling threats like denial-of-service, password spray, or brute force attacks. Azure AD B2C is built on the same technology as Microsoft Entra ID but for a different purpose and is a separate service. It allows businesses to build customer facing applications, and then allow anyone to sign up and sign in to those applications with no restrictions on user account.