You create an Azure Function. You want to protect the function using Azure AD authentication and create a custom connector. 
Please select three steps that you need to take before creating the custom connector.

Answer options:

A.Create Azure Function API definition
B.Configure Conditional Access
C.Register an app in Azure AD for Azure Function access
D.Create Azure AD Service principal
E.Create Azure AD Authentication for Azure Function

Correct Answers: A, C and E 
A custom connector is an API wrapper around the REST API. You can create such a wrapper for Azure Functions, Azure Web Apps, Azure API apps, etc. When you develop an application using one of these services, you need to describe the API`s operations by creating the API definitions before exporting the application`s APIs. You also need to set the authentication type for your custom connector.
Suppose you want to create a custom connector and export the Azure Function Web APIs. What is more, you want to protect access to the Azure Function with Azure AD authentication. And use the Azure AD authentication for the custom connector. 
After you create an Azure Function, you can use two options on the Azure Function App blade under the Settings section: Authentication (Number 1) or Authentication (classic) (Number 2). If you decide to use the Authentication (classic), the Azure portal will ask you to convert to the current Identity Provider Authentication (Number 3). You can select different providers on this screen, like Microsoft (including Azure AD identities) (Number 4), Facebook, Google, and Twitter. 

This Identity Provider registration also registers your Azure Function as an app within the Azure AD (Number 1) and defines the App Service settings (Number 2). 

Next, you need to register a new app, like Custom connector app, with the Azure AD and give access to your Azure Function. 

After that, you can create your API definition and create a custom connector. 
All other options are incorrect. 
For more information about the custom connector for the Azure AD protected Azure Function Web APIs, please visit the below URLs: 

https://docs.microsoft.com/en-us/azure/app-service/overview-authentication-authorization
https://docs.microsoft.com/en-us/azure/app-service/configure-authentication-provider-aad
https://docs.microsoft.com/en-us/connectors/custom-connectors/create-custom-connector-aad-protected-azure-functions