Library to help mapping id's, mainly for NFSv4.

When NFSv4 is using AUTH_GSS (which currently only supports Kerberos v5), the
NFSv4 server mapping functions MUST use secure communications.

We provide several mapping functions, configured using /etc/idmapd.conf

As of the 0.21 version of this library, mapping methods are separate
dynamically-loaded libaries.  This allows the separation of any
LDAP requirements from the main libnfsidmap library.  The main library
now basically loads and calls the functions in the method-specific
libaries.  The method libraries are expected to be named
"libnfsidmap_<method>.so", for example, "libnfsidmap_nsswitch.so".

Several methods may be specified in the /etc/idmapd.conf configuration
file.  Each method is called until a mapping is found.

The following translation methods are delivered in the default distribution:

nsswitch
--------

The default method is called nsswitch. This method uses the get password
file entry functions getpwname(), getpwid(), and the get group file entry
functions getgrnam(), getgrgid(). The nsswitch method can therefore be
configured by the /etc/nss_switch.conf passwd data base stanza. If secure
communications are required (AUTH_GSS), the passwd data base stanza can contain
the 'file' entry because the rpc.idmapd and rpc.svcgssd run as root, and/or the
'ldap' entry if the ldap service is configured to use SASL in /etc/ldap.conf.
The 'nis' entry is NOT recommended, it does not have a secure communications
mode.


static
------

This method works only for translating GSS authenticated names to local
names.  It uses a static mapping setup defined in the [Static] section
of the idmapd.conf file.  The form of the entries are:
  <GSS-Authenticated name> = <localuser>

For example:
  nfs/host.domain.org@DOMAIN.ORG = root

It is recommended that this module be used in combination with another
module (e.g. the nsswitch module).

umich_ldap
----------
An experimental method, umich_ldap uses an LDAP schema and ldap functions
to perform translations.  This method is designed to service remote users,
allowing remote users to set and get ACLs as well as map GSS principals
to id's.  The functions are LDAP based, and the ldap search filters look
for attribute names set by idmapd.conf [UMICH_SCHEMA]
NFSv4_name_attr, NFSv4_group_attr, and GSS_principal_attr.

It is assumed that the LDAP server will index these attributes, and that these
attributes will be associated with the nss.schema posixAccount uidNumber and
gidNumber.  We expect that the uidNumber and gidNumber attribute will be
configurable via the idmapd.conf file soon.

NFSv4_name_attr holds an NFSv4 name of the form user@domain, where the domain
portion of the name is a valid NFSv4 domain name. There is a one-to-one
mapping between the NFSv4_name_attr name and a UID.

NFSv4_group_attr holds an NFSv4 name of the form group@domain, where the domain
portion of the name is a valid NFSv4 domain name. There is a one-to-one
mapping between the NFSv4_group_attr name and a GID.

GSS_principal_attr holds a GSS security mechanism specific context principal
name. For Kerberos v5, it is a Kerberos principal <service/>principal@REALM.
For SPKM3, it is a PKI DN such as (line is split):`
"/C=US/ST=Michigan/O=University of Michigan/OU=UMICH Kerberos
 Certification Authority/CN=andros/USERID=andros/Email=andros@UMICH.EDU".
There is a many-to-one relationship between the GSS_principal_attr
name and a UID plus GID.

We have defined LDAP object classes for our experimental NFSv4 id mapping.
We made the attribute names configurable so that other sites could still use
the TR_UMICH_LDAP translation functions with different LDAP attribute names.

We use the same attribute name, NFSv4Name for the NFSv4_name_attr and the
NFSv4_group_attr. For local users and remote users that we wish to give
a local machine account, we add the NFSv4Name attribute and the GSSAuthName
attribute to the existing inetorgPerson and posixAccount schema.
For remote users that we do not wish to give a local machine account,
we use the NFSv4RemotePerson object to contain the NFSv4Name, uidNumber,
gidNumber, and GSSAuthName.

nfsv4.schema
------------
attributetype ( 1.3.6.1.4.1.250.1.61
        NAME ( 'NFSv4Name')
        DESC 'NFS version 4 Name'
        EQUALITY caseIgnoreIA5Match
        SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
        SINGLE-VALUE)

attributetype ( 1.3.6.1.4.1.250.1.62
        NAME ( 'GSSAuthName')
        DESC 'RPCSEC GSS authenticated user name'
        EQUALITY caseIgnoreIA5Match
        SYNTAX 1.3.6.1.4.1.1466.115.121.1.26)

#
# minimal information for NFSv4 access. used when local filesystem
# access is not permitted (nsswitch ldap calls fail), or when
# inetorgPerson is too much info.
#
objectclass ( 1.3.6.1.4.1.250.1.60 NAME 'NFSv4RemotePerson'
        DESC 'NFS version4 person from remote NFSv4 Domain'
        SUP top STRUCTURAL
        MUST ( uidNumber $ gidNumber $ NFSv4Name )
        MAY ( cn $ GSSAuthName $ description) )

#
# minimal information for NFSv4 access. used when local filesystem
# access is not permitted (nsswitch ldap calls fail), or when
# inetorgPerson is too much info.
#
objectclass ( 1.3.6.1.4.1.250.1.63 NAME 'NFSv4RemoteGroup'
        DESC 'NFS version4 group from remote NFSv4 Domain'
        SUP top STRUCTURAL
        MUST ( gidNumber $ NFSv4Name )
        MAY ( cn $ memberUid $ description) )