TrustAuthIncoming is a Microsoft Active Directory AttributeType
that is the password
used to validate protocol messages
flowing between the Trusted Domain Objects
TrustAuthIncoming is a secret attribute (MS-DRSR section 18.104.22.168.11, IsSecretAttribute), and are not readable outside of the context of the LSA on a Domain Controller.
There might be more information for this subject on one of the following: