What should be created in Azure AD to meet the requirements for Contoso developers?

To effectively meet the requirements for Contoso developers in Azure Active Directory (Azure AD), creating a synced user account in the corporate fabrikam.com domain is the most appropriate action. This solution enables developers to authenticate and have their access managed centrally within Azure AD, allowing for seamless integration with organizational resources and existing identity management processes.

By syncing user accounts from a domain like fabrikam.com, developers can leverage single sign-on (SSO) capabilities with Azure AD, which enhances productivity and security. This setup also provides the necessary control over user permissions and access to applications and services reliant on Azure AD, crucial for maintaining security in a development environment.

Having an external user account could permit some level of access, but it would not offer the same level of integration and central management as a synced user account would. A domain-joined computer is relevant for device management but does not directly fulfill the need to provide users' identities for accessing Azure resources. An application registration is aimed at configuring and managing applications rather than individual user identities, which further illustrates why a synced user account is the best solution.