How to find a specific API needed for a custom-developed application
Access to APIs require configuration of access scopes and roles. If you want to expose your resource application web APIs to client applications, configure access scopes and roles for the API. If you want a client application to access a web API, configure permissions to access the API in the app registration.
Configuring a resource application to expose web APIs
When you expose your web API, the API be displayed in the Select an API list when adding permissions to an app registration. To add access scopes, follow the steps outlined in Configure an application to expose web APIs.
Configuring a client application to access web APIs
When you add permissions to your app registration, you can add API access to exposed web APIs. To access web APIs, follow the steps outlined in Configure a client application to access web APIs.