You create a custom connector. 
Please select all types of authentication you can use when creating a connector from blank.

Answer options:

A.No authentication
B.Single Sign-On
C.Basic
D.Multi-factor
E.API Key
F.OAuth 2.0

Correct Answers: A, C, E and F 
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.
The custom connector wizard provides the four types of authentication: No authentication — no security for the API. Usually, this type is used for publicly exposed API.
Basic authentication — the basic security based on HTTP standards. This type requires users to provide the username and password for authentication.
API Key — the security based on a token that clients provide for making API calls. The token can be part of the query string or the request header.
OAuth 2.0 — the best security option for a custom connector. This type is based on specific authorization flows for applications and devices that providers define. The providers` list includes Azure AD, Basecamp, Dropbox, GitHub, Google, Instagram, Facebook, Salesforce, and others.
All other options are incorrect because the custom connector wizard does not provide these types of authentication. 
For more information about API authentication, please visit the below URLs: 

https://docs.microsoft.com/en-us/connectors/custom-connectors/
https://docs.microsoft.com/en-us/connectors/custom-connectors/#2-secure-your-api
https://docs.microsoft.com/en-us/connectors/custom-connectors/create-custom-connector-aad-protected-azure-functions