The iCal server uses the MD5 Digest authentication method by default. This does not allow Active directory users to log into the iCal server using their Active Directory credentials. It is strongly recommended that Kerberos be configured for Active Directory users. For customers who require a non-Kerberos solution to support Active Directory users, cleartext authentication can be enabled for the iCal service, as described below. For customers who choose to use cleartext authentication, Apple recommends the use of SSL to provide a more secure environment.

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Enabling iCal server access for users of Active Directory or third-party LDAP servers

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