The following subsections describe the authentication methods in more detail.
When trust
authentication is specified,
PostgreSQL™ assumes that anyone who can
connect to the server is authorized to access the database with
whatever database user name they specify (even superuser names).
Of course, restrictions made in the database
and
user
columns still apply.
This method should only be used when there is adequate
operating-system-level protection on connections to the server.
trust
authentication is appropriate and very
convenient for local connections on a single-user workstation. It
is usually not appropriate by itself on a multiuser
machine. However, you might be able to use trust
even
on a multiuser machine, if you restrict access to the server's
Unix-domain socket file using file-system permissions. To do this, set the
unix_socket_permissions
(and possibly
unix_socket_group
) configuration parameters as
described in the section called “Connections and Authentication”. Or you
could set the unix_socket_directories
configuration parameter to place the socket file in a suitably
restricted directory.
Setting file-system permissions only helps for Unix-socket connections.
Local TCP/IP connections are not restricted by file-system permissions.
Therefore, if you want to use file-system permissions for local security,
remove the host ... 127.0.0.1 ...
line from
pg_hba.conf
, or change it to a
non-trust
authentication method.
trust
authentication is only suitable for TCP/IP connections
if you trust every user on every machine that is allowed to connect
to the server by the pg_hba.conf
lines that specify
trust
. It is seldom reasonable to use trust
for any TCP/IP connections other than those from localhost
(127.0.0.1).
The password-based authentication methods are md5
and password
. These methods operate
similarly except for the way that the password is sent across the
connection, namely MD5-hashed and clear-text respectively.
If you are at all concerned about password
“sniffing” attacks then md5
is preferred.
Plain password
should always be avoided if possible.
However, md5
cannot be used with the db_user_namespace feature. If the connection is
protected by SSL encryption then password
can be used
safely (though SSL certificate authentication might be a better
choice if one is depending on using SSL).
PostgreSQL™ database passwords are
separate from operating system user passwords. The password for
each database user is stored in the pg_authid
system
catalog. Passwords can be managed with the SQL commands
CREATE USER(7) and
ALTER ROLE(7),
e.g., CREATE USER foo WITH PASSWORD 'secret'
.
If no password has been set up for a user, the stored password
is null and password authentication will always fail for that user.
GSSAPI™ is an industry-standard protocol for secure authentication defined in RFC 2743. PostgreSQL™ supports GSSAPI™ with Kerberos™ authentication according to RFC 1964. GSSAPI™ provides automatic authentication (single sign-on) for systems that support it. The authentication itself is secure, but the data sent over the database connection will be sent unencrypted unless SSL is used.
GSSAPI support has to be enabled when PostgreSQL™ is built; see Chapter 15, Installation from Source Code for more information.
When GSSAPI™ uses
Kerberos™, it uses a standard principal
in the format
.
The PostgreSQL server will accept any principal that is included in the keytab used by
the server, but care needs to be taken to specify the correct principal details when
making the connection from the client using the servicename
/hostname
@realm
krbsrvname
connection parameter. (See
also the section called “Parameter Key Words”.) The installation default can be
changed from the default postgres
at build time using
./configure --with-krb-srvnam=
whatever
.
In most environments,
this parameter never needs to be changed.
Some Kerberos implementations might require a different service name,
such as Microsoft Active Directory which requires the service name
to be in upper case (POSTGRES
).
hostname
is the fully qualified host name of the
server machine. The service principal's realm is the preferred realm
of the server machine.
Client principals must have their PostgreSQL™ database user
name as their first component, for example
pgusername@realm
. Alternatively, you can use a user name
mapping to map from the first component of the principal name to the
database user name. By default, the realm of the client is
not checked by PostgreSQL™. If you have cross-realm
authentication enabled and need to verify the realm, use the
krb_realm
parameter, or enable include_realm
and use user name mapping to check the realm.
Make sure that your server keytab file is readable (and preferably
only readable) by the PostgreSQL™ server
account. (See also the section called “The PostgreSQL™ User Account”.) The location
of the key file is specified by the krb_server_keyfile configuration
parameter. The default is
/usr/local/pgsql/etc/krb5.keytab
(or whatever
directory was specified as sysconfdir
at build time).
For security reasons, it is recommended to use a separate keytab
just for the PostgreSQL™ server rather
than opening up permissions on the system keytab file.
The keytab file is generated by the Kerberos software; see the Kerberos documentation for details. The following example is for MIT-compatible Kerberos 5 implementations:
kadmin%
ank -randkey postgres/server.my.domain.org
kadmin%
ktadd -k krb5.keytab postgres/server.my.domain.org
When connecting to the database make sure you have a ticket for a
principal matching the requested database user name. For example, for
database user name fred
, principal
fred@EXAMPLE.COM
would be able to connect. To also allow
principal fred/users.example.com@EXAMPLE.COM
, use a user name
map, as described in the section called “User Name Maps”.
The following configuration options are supported for GSSAPI™:
include_realm
If set to 1, the realm name from the authenticated user principal is included in the system user name that's passed through user name mapping (the section called “User Name Maps”). This is useful for handling users from multiple realms.
map
Allows for mapping between system and database user names. See
the section called “User Name Maps” for details. For a Kerberos
principal username/hostbased@EXAMPLE.COM
, the
user name used for mapping is username/hostbased
if include_realm
is disabled, and
username/hostbased@EXAMPLE.COM
if
include_realm
is enabled.
krb_realm
Sets the realm to match user principal names against. If this parameter is set, only users of that realm will be accepted. If it is not set, users of any realm can connect, subject to whatever user name mapping is done.
SSPI™ is a Windows™
technology for secure authentication with single sign-on.
PostgreSQL™ will use SSPI in
negotiate
mode, which will use
Kerberos™ when possible and automatically
fall back to NTLM™ in other cases.
SSPI™ authentication only works when both
server and client are running Windows™,
or, on non-Windows platforms, when GSSAPI™
is available.
When using Kerberos™ authentication, SSPI™ works the same way GSSAPI™ does; see the section called “GSSAPI Authentication” for details.
The following configuration options are supported for SSPI™:
include_realm
If set to 1, the realm name from the authenticated user principal is included in the system user name that's passed through user name mapping (the section called “User Name Maps”). This is useful for handling users from multiple realms.
map
Allows for mapping between system and database user names. See the section called “User Name Maps” for details.
krb_realm
Sets the realm to match user principal names against. If this parameter is set, only users of that realm will be accepted. If it is not set, users of any realm can connect, subject to whatever user name mapping is done.
The ident authentication method works by obtaining the client's operating system user name from an ident server and using it as the allowed database user name (with an optional user name mapping). This is only supported on TCP/IP connections.
When ident is specified for a local (non-TCP/IP) connection, peer authentication (see the section called “Peer Authentication”) will be used instead.
The following configuration options are supported for ident™:
map
Allows for mapping between system and database user names. See the section called “User Name Maps” for details.
The “Identification Protocol” is described in
RFC 1413. Virtually every Unix-like
operating system ships with an ident server that listens on TCP
port 113 by default. The basic functionality of an ident server
is to answer questions like “What user initiated the
connection that goes out of your port X
and connects to my port Y
?”.
Since PostgreSQL™ knows both X
and
Y
when a physical connection is established, it
can interrogate the ident server on the host of the connecting
client and can theoretically determine the operating system user
for any given connection.
The drawback of this procedure is that it depends on the integrity of the client: if the client machine is untrusted or compromised, an attacker could run just about any program on port 113 and return any user name he chooses. This authentication method is therefore only appropriate for closed networks where each client machine is under tight control and where the database and system administrators operate in close contact. In other words, you must trust the machine running the ident server. Heed the warning:
The Identification Protocol is not intended as an authorization or access control protocol. | ||
--RFC 1413 |
Some ident servers have a nonstandard option that causes the returned user name to be encrypted, using a key that only the originating machine's administrator knows. This option must not be used when using the ident server with PostgreSQL™, since PostgreSQL™ does not have any way to decrypt the returned string to determine the actual user name.
The peer authentication method works by obtaining the client's operating system user name from the kernel and using it as the allowed database user name (with optional user name mapping). This method is only supported on local connections.
The following configuration options are supported for peer™:
map
Allows for mapping between system and database user names. See the section called “User Name Maps” for details.
Peer authentication is only available on operating systems providing
the getpeereid()
function, the SO_PEERCRED
socket parameter, or similar mechanisms. Currently that includes
Linux
,
most flavors of BSD
including
OS X
,
and Solaris
.
This authentication method operates similarly to
password
except that it uses LDAP
as the password verification method. LDAP is used only to validate
the user name/password pairs. Therefore the user must already
exist in the database before LDAP can be used for
authentication.
LDAP authentication can operate in two modes. In the first mode,
which we will call the simple bind mode,
the server will bind to the distinguished name constructed as
prefix
username
suffix
.
Typically, the prefix
parameter is used to specify
cn=
, or DOMAIN
\
in an Active
Directory environment. suffix
is used to specify the
remaining part of the DN in a non-Active Directory environment.
In the second mode, which we will call the search+bind mode,
the server first binds to the LDAP directory with
a fixed user name and password, specified with ldapbinddn
and ldapbindpasswd
, and performs a search for the user trying
to log in to the database. If no user and password is configured, an
anonymous bind will be attempted to the directory. The search will be
performed over the subtree at ldapbasedn
, and will try to
do an exact match of the attribute specified in
ldapsearchattribute
.
Once the user has been found in
this search, the server disconnects and re-binds to the directory as
this user, using the password specified by the client, to verify that the
login is correct. This mode is the same as that used by LDAP authentication
schemes in other software, such as Apache mod_authnz_ldap and pam_ldap.
This method allows for significantly more flexibility
in where the user objects are located in the directory, but will cause
two separate connections to the LDAP server to be made.
The following configuration options are used in both modes:
ldapserver
Names or IP addresses of LDAP servers to connect to. Multiple servers may be specified, separated by spaces.
ldapport
Port number on LDAP server to connect to. If no port is specified, the LDAP library's default port setting will be used.
ldaptls
Set to 1 to make the connection between PostgreSQL and the LDAP server use TLS encryption. Note that this only encrypts the traffic to the LDAP server — the connection to the client will still be unencrypted unless SSL is used.
The following options are used in simple bind mode only:
ldapprefix
String to prepend to the user name when forming the DN to bind as, when doing simple bind authentication.
ldapsuffix
String to append to the user name when forming the DN to bind as, when doing simple bind authentication.
The following options are used in search+bind mode only:
ldapbasedn
Root DN to begin the search for the user in, when doing search+bind authentication.
ldapbinddn
DN of user to bind to the directory with to perform the search when doing search+bind authentication.
ldapbindpasswd
Password for user to bind to the directory with to perform the search when doing search+bind authentication.
ldapsearchattribute
Attribute to match against the user name in the search when doing
search+bind authentication. If no attribute is specified, the
uid
attribute will be used.
ldapurl
An RFC 4516 LDAP URL. This is an alternative way to write some of the other LDAP options in a more compact and standard form. The format is
ldap://host
[:port
]/basedn
[?[attribute
][?[scope
]]]
scope
must be one
of base
, one
, sub
,
typically the latter. Only one attribute is used, and some other
components of standard LDAP URLs such as filters and extensions are
not supported.
For non-anonymous binds, ldapbinddn
and ldapbindpasswd
must be specified as separate
options.
To use encrypted LDAP connections, the ldaptls
option has to be used in addition to ldapurl
.
The ldaps
URL scheme (direct SSL connection) is not
supported.
LDAP URLs are currently only supported with OpenLDAP, not on Windows.
It is an error to mix configuration options for simple bind with options for search+bind.
Here is an example for a simple-bind LDAP configuration:
host ... ldap ldapserver=ldap.example.net ldapprefix="cn=" ldapsuffix=", dc=example, dc=net"
When a connection to the database server as database
user someuser
is requested, PostgreSQL will attempt to
bind to the LDAP server using the DN cn=someuser, dc=example,
dc=net
and the password provided by the client. If that connection
succeeds, the database access is granted.
Here is an example for a search+bind configuration:
host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchattribute=uid
When a connection to the database server as database
user someuser
is requested, PostgreSQL will attempt to
bind anonymously (since ldapbinddn
was not specified) to
the LDAP server, perform a search for (uid=someuser)
under the specified base DN. If an entry is found, it will then attempt to
bind using that found information and the password supplied by the client.
If that second connection succeeds, the database access is granted.
Here is the same search+bind configuration written as a URL:
host ... ldap lapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
Some other software that supports authentication against LDAP uses the same URL format, so it will be easier to share the configuration.
Since LDAP often uses commas and spaces to separate the different parts of a DN, it is often necessary to use double-quoted parameter values when configuring LDAP options, as shown in the examples.
This authentication method operates similarly to
password
except that it uses RADIUS
as the password verification method. RADIUS is used only to validate
the user name/password pairs. Therefore the user must already
exist in the database before RADIUS can be used for
authentication.
When using RADIUS authentication, an Access Request message will be sent
to the configured RADIUS server. This request will be of type
Authenticate Only
, and include parameters for
user name
, password
(encrypted) and
NAS Identifier
. The request will be encrypted using
a secret shared with the server. The RADIUS server will respond to
this server with either Access Accept
or
Access Reject
. There is no support for RADIUS accounting.
The following configuration options are supported for RADIUS:
radiusserver
The name or IP address of the RADIUS server to connect to. This parameter is required.
radiussecret
The shared secret used when talking securely to the RADIUS server. This must have exactly the same value on the PostgreSQL and RADIUS servers. It is recommended that this be a string of at least 16 characters. This parameter is required.
The encryption vector used will only be cryptographically strong if PostgreSQL™ is built with support for OpenSSL™. In other cases, the transmission to the RADIUS server should only be considered obfuscated, not secured, and external security measures should be applied if necessary.
radiusport
The port number on the RADIUS server to connect to. If no port
is specified, the default port 1812
will be used.
radiusidentifier
The string used as NAS Identifier
in the RADIUS
requests. This parameter can be used as a second parameter
identifying for example which database user the user is attempting
to authenticate as, which can be used for policy matching on
the RADIUS server. If no identifier is specified, the default
postgresql
will be used.
This authentication method uses SSL client certificates to perform
authentication. It is therefore only available for SSL connections.
When using this authentication method, the server will require that
the client provide a valid certificate. No password prompt will be sent
to the client. The cn
(Common Name) attribute of the
certificate
will be compared to the requested database user name, and if they match
the login will be allowed. User name mapping can be used to allow
cn
to be different from the database user name.
The following configuration options are supported for SSL certificate authentication:
map
Allows for mapping between system and database user names. See the section called “User Name Maps” for details.
This authentication method operates similarly to
password
except that it uses PAM (Pluggable
Authentication Modules) as the authentication mechanism. The
default PAM service name is postgresql
.
PAM is used only to validate user name/password pairs.
Therefore the user must already exist in the database before PAM
can be used for authentication. For more information about
PAM, please read the Linux-PAM™ Page.
The following configuration options are supported for PAM:
pamservice
PAM service name.
If PAM is set up to read /etc/shadow
, authentication
will fail because the PostgreSQL server is started by a non-root
user. However, this is not an issue when PAM is configured to use
LDAP or other authentication methods.