Security and authorization are critical aspects of Web API development to protect resources and ensure that only authorized clients can access them. In ASP.NET Core, you can implement security and authorization by using authentication middleware and authorization policies. Authentication middleware, such as JWT bearer authentication or OAuth 2.0 authentication, validates the identity of the client. Authorization policies, defined using attributes or policy-based approaches, control access to specific resources or actions based on roles, claims, or other criteria. You can integrate with external authentication providers like Azure AD, Google, or Facebook using authentication middleware. Additionally, you can implement custom authorization logic by creating authorization handlers and policies. Implementing security and authorization ensures that your Web API is protected and accessible only to authenticated and authorized users.