I would like to offer a word of caution in authenticating against
multiple directories.  It is vitally important to ensure that the
value of the CAS principal ID is globally unique across all
authentication sources, otherwise you are liable to authorization
problems similar to impersonation attacks.  This arises because CAS
clients typically only have the principal ID (username) to identify
the user; if the same username exists in multiple authentication
sources, there is ambiguity about the human principal corresponding to
that identifier.  If you cannot guarantee uniqueness in your principal
ID namespace, you would need to have CAS clients requesting SAML to
obtain additional attributes that uniquely identify the user.

While the format of mail and sAMAccountName are sufficiently different
to guarantee uniqueness from one another, there are no restrictions on
the mail attribute that would prevent duplication unless you have some
provisioning process that prevents it.  Contrast that to
sAMAccountName which is constrained by AD to be unique within a
domain.

M

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