A is incorrect: Identity providers are responsible for authenticating users and providing identity information. They are not directly related to defining the global blueprint of an application, including Redirect URIs, Supported account types, and Exposed API scopes in the Microsoft Entra admin center.
B is correct: App registrations are used to define the global blueprint of an application, including Redirect URIs, Supported account types, and Exposed API scopes. They are created and managed in the App registrations blade of the Microsoft Entra admin center, making this choice the correct option for defining the specified parameters.
C is incorrect: The Enterprise applications page in the Microsoft Entra admin center is used to manage applications that have been integrated with the tenant for single sign-on and other purposes. It is not the correct location for defining the initial configuration details of a custom line-of-business web API and SPA using Microsoft Entra ID.
D is incorrect: Conditional Access policies are used to enforce specific conditions for accessing resources within the organization. While they play a role in security and access control, they are not the appropriate location for defining the global blueprint of an application, including Redirect URIs, Supported account types, and Exposed API scopes in the Microsoft Entra admin center.