Client Authentication
client authentication
When a client application connects to the database server, it
specifies which PostgreSQL database user name it
wants to connect as, much the same way one logs into a Unix computer
as a particular user. Within the SQL environment the active database
user name determines access privileges to database objects — see
for more information. Therefore, it is
essential to restrict which database users can connect.
As explained in ,
PostgreSQL actually does privilege
management in terms of roles. In this chapter, we
consistently use database user to mean role with the
LOGIN privilege
.
Authentication is the process by which the
database server establishes the identity of the client, and by
extension determines whether the client application (or the user
who runs the client application) is permitted to connect with the
database user name that was requested.
PostgreSQL offers a number of different
client authentication methods. The method used to authenticate a
particular client connection can be selected on the basis of
(client) host address, database, and user.
PostgreSQL database user names are logically
separate from user names of the operating system in which the server
runs. If all the users of a particular server also have accounts on
the server's machine, it makes sense to assign database user names
that match their operating system user names. However, a server that
accepts remote connections might have many database users who have no local
operating system
account, and in such cases there need be no connection between
database user names and OS user names.
The <filename>pg_hba.conf</filename> File
pg_hba.conf
Client authentication is controlled by a configuration file,
which traditionally is named
pg_hba.conf and is stored in the database
cluster's data directory.
(HBA stands for host-based authentication.) A default
pg_hba.conf file is installed when the data
directory is initialized by initdb. It is
possible to place the authentication configuration file elsewhere,
however; see the configuration parameter.
The general format of the pg_hba.conf file is
a set of records, one per line. Blank lines are ignored, as is any
text after the # comment character.
Records cannot be continued across lines.
A record is made
up of a number of fields which are separated by spaces and/or tabs.
Fields can contain white space if the field value is double-quoted.
Quoting one of the keywords in a database, user, or address field (e.g.,
all or replication) makes the word lose its special
meaning, and just match a database, user, or host with that name.
Each record specifies a connection type, a client IP address range
(if relevant for the connection type), a database name, a user name,
and the authentication method to be used for connections matching
these parameters. The first record with a matching connection type,
client address, requested database, and user name is used to perform
authentication. There is no fall-through or
backup: if one record is chosen and the authentication
fails, subsequent records are not considered. If no record matches,
access is denied.
A record can have one of the seven formats
local database user auth-method auth-options
host database user address auth-method auth-options
hostssl database user address auth-method auth-options
hostnossl database user address auth-method auth-options
host database user IP-address IP-mask auth-method auth-options
hostssl database user IP-address IP-mask auth-method auth-options
hostnossl database user IP-address IP-mask auth-method auth-options
The meaning of the fields is as follows:
local
This record matches connection attempts using Unix-domain
sockets. Without a record of this type, Unix-domain socket
connections are disallowed.
host
This record matches connection attempts made using TCP/IP.
host records match either
SSL or non-SSL connection
attempts.
Remote TCP/IP connections will not be possible unless
the server is started with an appropriate value for the
configuration parameter,
since the default behavior is to listen for TCP/IP connections
only on the local loopback address localhost.
hostssl
This record matches connection attempts made using TCP/IP,
but only when the connection is made with SSL
encryption.
To make use of this option the server must be built with
SSL support. Furthermore,
SSL must be enabled at server start time
by setting the configuration parameter (see
for more information).
hostnossl
This record type has the opposite behavior of hostssl;
it only matches connection attempts made over
TCP/IP that do not use SSL.
database
Specifies which database name(s) this record matches. The value
all specifies that it matches all databases.
The value sameuser specifies that the record
matches if the requested database has the same name as the
requested user. The value samerole specifies that
the requested user must be a member of the role with the same
name as the requested database. (samegroup is an
obsolete but still accepted spelling of samerole.)
Superusers are not considered to be members of a role for the
purposes of samerole unless they are explicitly
members of the role, directly or indirectly, and not just by
virtue of being a superuser.
The value replication specifies that the record
matches if a replication connection is requested (note that
replication connections do not specify any particular database).
Otherwise, this is the name of
a specific PostgreSQL database.
Multiple database names can be supplied by separating them with
commas. A separate file containing database names can be specified by
preceding the file name with @.
user
Specifies which database user name(s) this record
matches. The value all specifies that it
matches all users. Otherwise, this is either the name of a specific
database user, or a group name preceded by +.
(Recall that there is no real distinction between users and groups
in PostgreSQL; a + mark really means
match any of the roles that are directly or indirectly members
of this role, while a name without a + mark matches
only that specific role.) For this purpose, a superuser is only
considered to be a member of a role if they are explicitly a member
of the role, directly or indirectly, and not just by virtue of
being a superuser.
Multiple user names can be supplied by separating them with commas.
A separate file containing user names can be specified by preceding the
file name with @.
address
Specifies the client machine address(es) that this record
matches. This field can contain either a host name, an IP
address range, or one of the special key words mentioned below.
An IP address range is specified using standard numeric notation
for the range's starting address, then a slash (/)
and a CIDR mask length. The mask
length indicates the number of high-order bits of the client
IP address that must match. Bits to the right of this should
be zero in the given IP address.
There must not be any white space between the IP address, the
/, and the CIDR mask length.
Typical examples of an IPv4 address range specified this way are
172.20.143.89/32 for a single host, or
172.20.143.0/24 for a small network, or
10.6.0.0/16 for a larger one.
An IPv6 address range might look like ::1/128
for a single host (in this case the IPv6 loopback address) or
fe80::7a31:c1ff:0000:0000/96 for a small
network.
0.0.0.0/0 represents all
IPv4 addresses, and ::0/0 represents
all IPv6 addresses.
To specify a single host, use a mask length of 32 for IPv4 or
128 for IPv6. In a network address, do not omit trailing zeroes.
An entry given in IPv4 format will match only IPv4 connections,
and an entry given in IPv6 format will match only IPv6 connections,
even if the represented address is in the IPv4-in-IPv6 range.
Note that entries in IPv6 format will be rejected if the system's
C library does not have support for IPv6 addresses.
You can also write all to match any IP address,
samehost to match any of the server's own IP
addresses, or samenet to match any address in any
subnet that the server is directly connected to.
If a host name is specified (anything that is not an IP address
range or a special key word is treated as a host name),
that name is compared with the result of a reverse name
resolution of the client's IP address (e.g., reverse DNS
lookup, if DNS is used). Host name comparisons are case
insensitive. If there is a match, then a forward name
resolution (e.g., forward DNS lookup) is performed on the host
name to check whether any of the addresses it resolves to are
equal to the client's IP address. If both directions match,
then the entry is considered to match. (The host name that is
used in pg_hba.conf should be the one that
address-to-name resolution of the client's IP address returns,
otherwise the line won't be matched. Some host name databases
allow associating an IP address with multiple host names, but
the operating system will only return one host name when asked
to resolve an IP address.)
A host name specification that starts with a dot
(.) matches a suffix of the actual host
name. So .example.com would match
foo.example.com (but not just
example.com).
When host names are specified
in pg_hba.conf, you should make sure that
name resolution is reasonably fast. It can be of advantage to
set up a local name resolution cache such
as nscd. Also, you may wish to enable the
configuration parameter log_hostname to see
the client's host name instead of the IP address in the log.
This field only applies to host,
hostssl, and hostnossl records.
Users sometimes wonder why host names are handled
in this seemingly complicated way, with two name resolutions
including a reverse lookup of the client's IP address. This
complicates use of the feature in case the client's reverse DNS
entry is not set up or yields some undesirable host name.
It is done primarily for efficiency: this way, a connection attempt
requires at most two resolver lookups, one reverse and one forward.
If there is a resolver problem with some address, it becomes only
that client's problem. A hypothetical alternative
implementation that only did forward lookups would have to
resolve every host name mentioned in
pg_hba.conf during every connection attempt.
That could be quite slow if many names are listed.
And if there is a resolver problem with one of the host names,
it becomes everyone's problem.
Also, a reverse lookup is necessary to implement the suffix
matching feature, because the actual client host name needs to
be known in order to match it against the pattern.
Note that this behavior is consistent with other popular
implementations of host name-based access control, such as the
Apache HTTP Server and TCP Wrappers.
IP-address
IP-mask
These two fields can be used as an alternative to the
IP-address/mask-length
notation. Instead of
specifying the mask length, the actual mask is specified in a
separate column. For example, 255.0.0.0 represents an IPv4
CIDR mask length of 8, and 255.255.255.255 represents a
CIDR mask length of 32.
These fields only apply to host,
hostssl, and hostnossl records.
auth-method
Specifies the authentication method to use when a connection matches
this record. The possible choices are summarized here; details
are in .
trust
Allow the connection unconditionally. This method
allows anyone that can connect to the
PostgreSQL database server to login as
any PostgreSQL user they wish,
without the need for a password or any other authentication. See for details.
reject
Reject the connection unconditionally. This is useful for
filtering out certain hosts from a group, for example a
reject line could block a specific host from connecting,
while a later line allows the remaining hosts in a specific
network to connect.
md5
Require the client to supply a double-MD5-hashed password for
authentication.
See for details.
password
Require the client to supply an unencrypted password for
authentication.
Since the password is sent in clear text over the
network, this should not be used on untrusted networks.
See for details.
gss
Use GSSAPI to authenticate the user. This is only
available for TCP/IP connections. See for details.
sspi
Use SSPI to authenticate the user. This is only
available on Windows. See for details.
ident
Obtain the operating system user name of the client
by contacting the ident server on the client
and check if it matches the requested database user name.
Ident authentication can only be used on TCP/IP
connections. When specified for local connections, peer
authentication will be used instead.
See for details.
peer
Obtain the client's operating system user name from the operating
system and check if it matches the requested database user name.
This is only available for local connections.
See for details.
ldap
Authenticate using an LDAP server. See for details.
radius
Authenticate using a RADIUS server. See for details.
cert
Authenticate using SSL client certificates. See
for details.
pam
Authenticate using the Pluggable Authentication Modules
(PAM) service provided by the operating system. See for details.
auth-options
After the auth-method field, there can be field(s) of
the form name=value that
specify options for the authentication method. Details about which
options are available for which authentication methods appear below.
Files included by @ constructs are read as lists of names,
which can be separated by either whitespace or commas. Comments are
introduced by #, just as in
pg_hba.conf, and nested @ constructs are
allowed. Unless the file name following @ is an absolute
path, it is taken to be relative to the directory containing the
referencing file.
Since the pg_hba.conf records are examined
sequentially for each connection attempt, the order of the records is
significant. Typically, earlier records will have tight connection
match parameters and weaker authentication methods, while later
records will have looser match parameters and stronger authentication
methods. For example, one might wish to use trust
authentication for local TCP/IP connections but require a password for
remote TCP/IP connections. In this case a record specifying
trust authentication for connections from 127.0.0.1 would
appear before a record specifying password authentication for a wider
range of allowed client IP addresses.
The pg_hba.conf file is read on start-up and when
the main server process receives a
SIGHUPSIGHUP
signal. If you edit the file on an
active system, you will need to signal the postmaster
(using pg_ctl reload or kill -HUP) to make it
re-read the file.
To connect to a particular database, a user must not only pass the
pg_hba.conf checks, but must have the
CONNECT privilege for the database. If you wish to
restrict which users can connect to which databases, it's usually
easier to control this by granting/revoking CONNECT privilege
than to put the rules in pg_hba.conf entries.
Some examples of pg_hba.conf entries are shown in
. See the next section for details on the
different authentication methods.
Example <filename>pg_hba.conf</filename> Entries
# Allow any user on the local system to connect to any database with
# any database user name using Unix-domain sockets (the default for local
# connections).
#
# TYPE DATABASE USER ADDRESS METHOD
local all all trust
# The same using local loopback TCP/IP connections.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 127.0.0.1/32 trust
# The same as the previous line, but using a separate netmask column
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host all all 127.0.0.1 255.255.255.255 trust
# The same over IPv6.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all ::1/128 trust
# The same using a host name (would typically cover both IPv4 and IPv6).
#
# TYPE DATABASE USER ADDRESS METHOD
host all all localhost trust
# Allow any user from any host with IP address 192.168.93.x to connect
# to database "postgres" as the same user name that ident reports for
# the connection (typically the operating system user name).
#
# TYPE DATABASE USER ADDRESS METHOD
host postgres all 192.168.93.0/24 ident
# Allow any user from host 192.168.12.10 to connect to database
# "postgres" if the user's password is correctly supplied.
#
# TYPE DATABASE USER ADDRESS METHOD
host postgres all 192.168.12.10/32 md5
# Allow any user from hosts in the example.com domain to connect to
# any database if the user's password is correctly supplied.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all .example.com md5
# In the absence of preceding "host" lines, these two lines will
# reject all connections from 192.168.54.1 (since that entry will be
# matched first), but allow GSSAPI connections from anywhere else
# on the Internet. The zero mask causes no bits of the host IP
# address to be considered, so it matches any host.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 192.168.54.1/32 reject
host all all 0.0.0.0/0 gss
# Allow users from 192.168.x.x hosts to connect to any database, if
# they pass the ident check. If, for example, ident says the user is
# "bryanh" and he requests to connect as PostgreSQL user "guest1", the
# connection is allowed if there is an entry in pg_ident.conf for map
# "omicron" that says "bryanh" is allowed to connect as "guest1".
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 192.168.0.0/16 ident map=omicron
# If these are the only three lines for local connections, they will
# allow local users to connect only to their own databases (databases
# with the same name as their database user name) except for administrators
# and members of role "support", who can connect to all databases. The file
# $PGDATA/admins contains a list of names of administrators. Passwords
# are required in all cases.
#
# TYPE DATABASE USER ADDRESS METHOD
local sameuser all md5
local all @admins md5
local all +support md5
# The last two lines above can be combined into a single line:
local all @admins,+support md5
# The database column can also use lists and file names:
local db1,db2,@demodbs all md5
User Name Maps
User name maps
When using an external authentication system like Ident or GSSAPI,
the name of the operating system user that initiated the connection
might not be the same as the database user he needs to connect as.
In this case, a user name map can be applied to map the operating system
user name to a database user. To use user name mapping, specify
map=map-name
in the options field in pg_hba.conf. This option is
supported for all authentication methods that receive external user names.
Since different mappings might be needed for different connections,
the name of the map to be used is specified in the
map-name parameter in pg_hba.conf
to indicate which map to use for each individual connection.
User name maps are defined in the ident map file, which by default is named
pg_ident.confpg_ident.conf
and is stored in the
cluster's data directory. (It is possible to place the map file
elsewhere, however; see the
configuration parameter.)
The ident map file contains lines of the general form:
map-name system-username database-username
Comments and whitespace are handled in the same way as in
pg_hba.conf. The
map-name is an arbitrary name that will be used to
refer to this mapping in pg_hba.conf. The other
two fields specify an operating system user name and a matching
database user name. The same map-name can be
used repeatedly to specify multiple user-mappings within a single map.
There is no restriction regarding how many database users a given
operating system user can correspond to, nor vice versa. Thus, entries
in a map should be thought of as meaning this operating system
user is allowed to connect as this database user
, rather than
implying that they are equivalent. The connection will be allowed if
there is any map entry that pairs the user name obtained from the
external authentication system with the database user name that the
user has requested to connect as.
If the system-username field starts with a slash (/),
the remainder of the field is treated as a regular expression.
(See for details of
PostgreSQL's regular expression syntax.) The regular
expression can include a single capture, or parenthesized subexpression,
which can then be referenced in the database-username
field as \1 (backslash-one). This allows the mapping of
multiple user names in a single line, which is particularly useful for
simple syntax substitutions. For example, these entries
mymap /^(.*)@mydomain\.com$ \1
mymap /^(.*)@otherdomain\.com$ guest
will remove the domain part for users with system user names that end with
@mydomain.com, and allow any user whose system name ends with
@otherdomain.com to log in as guest.
Keep in mind that by default, a regular expression can match just part of
a string. It's usually wise to use ^ and $, as
shown in the above example, to force the match to be to the entire
system user name.
The pg_ident.conf file is read on start-up and
when the main server process receives a
SIGHUPSIGHUP
signal. If you edit the file on an
active system, you will need to signal the postmaster
(using pg_ctl reload or kill -HUP) to make it
re-read the file.
A pg_ident.conf file that could be used in
conjunction with the pg_hba.conf file in is shown in . In this example, anyone
logged in to a machine on the 192.168 network that does not have the
operating system user name bryanh, ann, or
robert would not be granted access. Unix user
robert would only be allowed access when he tries to
connect as PostgreSQL user bob, not
as robert or anyone else. ann would
only be allowed to connect as ann. User
bryanh would be allowed to connect as either
bryanh or as guest1.
An Example <filename>pg_ident.conf</> File
# MAPNAME SYSTEM-USERNAME PG-USERNAME
omicron bryanh bryanh
omicron ann ann
# bob has user name robert on these machines
omicron robert bob
# bryanh can also connect as guest1
omicron bryanh guest1
Authentication Methods
The following subsections describe the authentication methods in more detail.
Trust Authentication
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 . 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).
Password Authentication
MD5
password
authentication
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 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
and
,
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 Authentication
GSSAPI
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 for more information.
When GSSAPI uses
Kerberos, it uses a standard principal
in the format
servicename/hostname@realm.
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 krbsrvname connection parameter. (See
also .) 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 location
of the key file is specified by the 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 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 (). This is
the recommended configuration as, otherwise, it is impossible to
differentiate users with the same username who are from different
realms. The default for this parameter is 0 (meaning to not include
the realm in the system user name) but may change to 1 in a future
version of PostgreSQL. Users can set it
explicitly to avoid any issues when upgrading.
map
Allows for mapping between system and database user names. See
for details. For a GSSAPI/Kerberos
principal, such as username@EXAMPLE.COM (or, less
commonly, username/hostbased@EXAMPLE.COM), the
default user name used for mapping is
username (or username/hostbased,
respectively), unless include_realm has been set to
1 (as recommended, see above), in which case
username@EXAMPLE.COM (or
username/hostbased@EXAMPLE.COM)
is what is seen as the system username when mapping.
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 Authentication
SSPI
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
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 (). This is
the recommended configuration as, otherwise, it is impossible to
differentiate users with the same username who are from different
realms. The default for this parameter is 0 (meaning to not include
the realm in the system user name) but may change to 1 in a future
version of PostgreSQL. Users can set it
explicitly to avoid any issues when upgrading.
map
Allows for mapping between system and database user names. See
for details. For a SSPI/Kerberos
principal, such as username@EXAMPLE.COM (or, less
commonly, username/hostbased@EXAMPLE.COM), the
default user name used for mapping is
username (or username/hostbased,
respectively), unless include_realm has been set to
1 (as recommended, see above), in which case
username@EXAMPLE.COM (or
username/hostbased@EXAMPLE.COM)
is what is seen as the system username when mapping.
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.
Ident Authentication
ident
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 ) will be
used instead.
The following configuration options are supported for ident:
map
Allows for mapping between system and database user names. See
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:
RFC 1413
The Identification Protocol is not intended as an authorization
or access control protocol.
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.
Peer Authentication
peer
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
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.
LDAP Authentication
LDAP
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 ldapurl="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.
RADIUS Authentication
RADIUS
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.
Certificate Authentication
Certificate
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
for details.
PAM Authentication
PAM
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.
Authentication Problems
Authentication failures and related problems generally
manifest themselves through error messages like the following:
FATAL: no pg_hba.conf entry for host "123.123.123.123", user "andym", database "testdb"
This is what you are most likely to get if you succeed in contacting
the server, but it does not want to talk to you. As the message
suggests, the server refused the connection request because it found
no matching entry in its pg_hba.conf
configuration file.
FATAL: password authentication failed for user "andym"
Messages like this indicate that you contacted the server, and it is
willing to talk to you, but not until you pass the authorization
method specified in the pg_hba.conf file. Check
the password you are providing, or check your Kerberos or ident
software if the complaint mentions one of those authentication
types.
FATAL: user "andym" does not exist
The indicated database user name was not found.
FATAL: database "testdb" does not exist
The database you are trying to connect to does not exist. Note that
if you do not specify a database name, it defaults to the database
user name, which might or might not be the right thing.
The server log might contain more information about an
authentication failure than is reported to the client. If you are
confused about the reason for a failure, check the server log.