Which authentication scheme is recommended for securing custom connectors deployed with Azure Functions?

Using Azure Active Directory OAuth 2.0 as the authentication scheme for securing custom connectors deployed with Azure Functions is recommended because it provides a robust and secure method of managing access to your applications and APIs. Azure Active Directory (AAD) offers centralized identity management and enables applications to authenticate users using industry-standard protocols, enhancing security.

OAuth 2.0 enables token-based authentication, which means that users do not need to share their credentials with the application; instead, they receive an access token after authenticating. This token can be used to access the Azure Function securely, ensuring that only authorized users or applications can invoke the function. Additionally, AAD allows for fine-grained access control and supports single sign-on (SSO), improving the user experience and security for applications integrated with the connector.

The other authentication methods, while possible, do not provide the same level of secure and manageable access as OAuth 2.0. For instance, no authentication leaves the application vulnerable, while basic authentication exposes user credentials, and Windows authentication can limit accessibility, especially in cloud environments where users may not operate within a Windows domain. Thus, the use of OAuth 2.0 with Azure Active Directory ensures the highest degree of security and maintainability for custom connectors.