The Access Control Identifier (ACI) part of an ACL entry specifies the
user or group for which the entry applies. Group identifiers are
distinguished be the prefix "group:". For example, "group:accounting".
There are two special identifiers, "anonymous", and "anyone", which are
explained below. The meaning of other identifiers usually depends on
the authorization mechanism being used (selected by
compile time, defaulting to Unix).
With any authorization mechanism, two special identifiers are defined.
anonymous refers to the anonymous, or unauthenticated
user. The identifier
anyone refers to all users, including the
anyone may commonly be used with the post
p to allow message insertion to mailboxes.
Kerberos vs. Unix Authorization
The Cyrus IMAP server comes with four authorization mechanisms, one is
compatible with Unix-style (
/etc/passwd) authorization, one for use
with Kerberos 4, one for use with Kerberos 5, and one for use with an
external authorization process (ptloader) which can interface with
other group databases (e.g. AFS PTS groups, LDAP Groups, etc).
Authentication !== Authorization
Note that authorization is not the same thing as authentication.
Authentication is the act of proving who you are. Authorization is
the act of determining what rights you have. Authentication is
discussed in the Login Authentication part of
In the Unix authorization mechanism, ACIs are either a valid userid or
group: followed by a group listed in
root Refers to the user root
group:staff Refers to the group staff
It is also possible to use unix groups with users authenticated through
a non-/etc/passwd backend. Note that using unix groups in this way
/etc/passwd entries) is not recommended.
Cyrus requires the getgrent(3) POSIX sysctl. As such, NSS needs to
be configured to have the groups available, one of which includes
"files", but could also include "ldap".
NSS augmentations, such as
may be used to provide Cyrus access to group information via NSS.
Using the Kerberos authorization mechanism, ACIs are of the form:
$instance is omitted, it defaults to the null string. If
$realm is omitted, it defaults to the local realm.
/etc/krb.equiv contains mappings between Kerberos
principals. The file contains zero or more lines, each containing two
fields. Any identity matching the first field of a line is changed to
the second identity during canonicalization. For example, a line in
will cause the identity
bovik@REMOTE.COM to be treated as if it
were the local identity
A site may wish to write their own authorization mechanism, perhaps to
implement a local group mechanism. If it does so (by implementing an
auth_[whatever] PTS module), it will dictate its own form and
meaning of identifiers.