Authentication is not exactly correct on how it explains the default authentication works.

Default authentication works in following way:

• It is not possible to select LDAP if it is not configured in LDAP tab.
• It is not possible to use internal authentication, if at least one of user's usergroups is set to LDAP authentication method.
• HTTP and SAML authentication methods are additional options, how user can log in in addition to Internal or LDAP authentication. You can't set them as default authentication methods.