The AuthType directive is used to specify the method of authentication for a directory or a location on the Apache HTTPD server. The directive has four possible values: None, Basic, Digest, and Form. Each value corresponds to a different module that implements the authentication mechanism.

None: This value means that no authentication is required. This is the default value and it can be used to override any inherited authentication settings.

Basic: This value means that the basic authentication method is used. This method is implemented by the mod_auth_basic module. It requires the user to enter a username and a password, which are sent to the server in plain text. Therefore, this method is not very secure and should be used with encryption, such as SSL or TLS.

Digest: This value means that the digest authentication method is used. This method is implemented by the mod_auth_digest module. It requires the user to enter a username and a password, which are hashed by the client and the server using a nonce (a random number) and a realm (a name for the protected area). Therefore, this method is more secure than the basic method, as it prevents replay attacks and password sniffing.

Form: This value means that the form authentication method is used. This method is implemented by the mod_auth_form module. It requires the user to fill out a web form with their credentials, which are sent to the server using the POST method. Therefore, this method is more flexible and user-friendly than the other methods, as it allows the use of custom forms and cookies.

References:

AuthType Directive

Authentication and Authorization - Apache HTTP Server Version 2.4

How to Create and Use .htpasswd