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 MDASH see [???](#user-manag) for more
information. Therefore, it is essential to restrict which database users
can connect.

> **Note**
>
> As explained in [???](#user-manag), 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 `pg_hba.conf` File {#auth-pg-hba-conf}
======================

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 [???](#guc-hba-file)
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. A record can be continued onto the next line by ending the
line with a backslash. (Backslashes are not special except at the end of
a line.) 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. Backslash line continuation applies even within quoted text or
comments.

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 several 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 \[auth-options\] hostgssenc database
user address auth-method \[auth-options\] hostnogssenc 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 \[auth-options\] hostgssenc database user IP-address
IP-mask auth-method \[auth-options\] hostnogssenc 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 SSL or non-SSL connection attempts as well as GSSAPI
    encrypted or non-GSSAPI encrypted connection attempts.

    > **Note**
    >
    > Remote TCP/IP connections will not be possible unless the server
    > is started with an appropriate value for the
    > [???](#guc-listen-addresses) 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 by setting the
    [???](#guc-ssl) configuration parameter (see [???](#ssl-tcp) for
    more information). Otherwise, the `hostssl` record is ignored except
    for logging a warning that it cannot match any connections.

`hostnossl`

:   This record type has the opposite behavior of `hostssl`; it only
    matches connection attempts made over TCP/IP that do not use SSL.

`hostgssenc`

:   This record matches connection attempts made using TCP/IP, but only
    when the connection is made with GSSAPI encryption.

    To make use of this option the server must be built with GSSAPI
    support. Otherwise, the `hostgssenc` record is ignored except for
    logging a warning that it cannot match any connections.

`hostnogssenc`

:   This record type has the opposite behavior of `hostgssenc`; it only
    matches connection attempts made over TCP/IP that do not use GSSAPI
    encryption.

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 physical replication connection is
    requested, however, it doesn\'t match with logical replication
    connections. Note that physical replication connections do not
    specify any particular database whereas logical replication
    connections do specify it. 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.

    These fields do not apply to `local` records.

    > **Note**
    >
    > 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 do not apply to `local` records.

auth-method

:   Specifies the authentication method to use when a connection matches
    this record. The possible choices are summarized here; details are
    in [Authentication Methods](#auth-methods).

    `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 [Trust
        Authentication](#auth-trust) 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.

    `scram-sha-256`

    :   Perform SCRAM-SHA-256 authentication to verify the user\'s
        password. See [Password Authentication](#auth-password) for
        details.

    `md5`

    :   Perform SCRAM-SHA-256 or MD5 authentication to verify the
        user\'s password. See [Password Authentication](#auth-password)
        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
        [Password Authentication](#auth-password) for details.

    `gss`

    :   Use GSSAPI to authenticate the user. This is only available for
        TCP/IP connections. See [GSSAPI Authentication](#gssapi-auth)
        for details. It can be used in conjunction with GSSAPI
        encryption.

    `sspi`

    :   Use SSPI to authenticate the user. This is only available on
        Windows. See [SSPI Authentication](#sspi-auth) 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
        [Ident Authentication](#auth-ident) 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
        [Peer Authentication](#auth-peer) for details.

    `ldap`

    :   Authenticate using an LDAP server. See [LDAP
        Authentication](#auth-ldap) for details.

    `radius`

    :   Authenticate using a RADIUS server. See [RADIUS
        Authentication](#auth-radius) for details.

    `cert`

    :   Authenticate using SSL client certificates. See [Certificate
        Authentication](#auth-cert) for details.

    `pam`

    :   Authenticate using the Pluggable Authentication Modules (PAM)
        service provided by the operating system. See [PAM
        Authentication](#auth-pam) for details.

    `bsd`

    :   Authenticate using the BSD Authentication service provided by
        the operating system. See [BSD Authentication](#auth-bsd) 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.

    In addition to the method-specific options listed below, there is a
    method-independent authentication option `clientcert`, which can be
    specified in any `hostssl` record. This option can be set to
    `verify-ca` or `verify-full`. Both options require the client to
    present a valid (trusted) SSL certificate, while `verify-full`
    additionally enforces that the `cn` (Common Name) in the certificate
    matches the username or an applicable mapping. This behavior is
    similar to the `cert` authentication method (see [Certificate
    Authentication](#auth-cert)) but enables pairing the verification of
    client certificates with any authentication method that supports
    `hostssl` entries.

    On any record using client certificate authentication (i.e. one
    using the `cert` authentication method or one using the `clientcert`
    option), you can specify which part of the client certificate
    credentials to match using the `clientname` option. This option can
    have one of two values. If you specify `clientname=CN`, which is the
    default, the username is matched against the certificate\'s
    `Common Name (CN)`. If instead you specify `clientname=DN` the
    username is matched against the entire `Distinguished Name (DN)` of
    the certificate. This option is probably best used in conjunction
    with a username map. The comparison is done with the `DN` in [RFC
    2253](https://tools.ietf.org/html/rfc2253) format. To see the `DN`
    of a client certificate in this format, do

        openssl x509 -in myclient.crt -noout --subject -nameopt RFC2253 | sed "s/^subject=//"

    Care needs to be taken when using this option, especially when using
    regular expression matching against the `DN`.

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`, calling the SQL function `pg_reload_conf()`, or using
`kill
   -HUP`) to make it re-read the file.

> **Note**
>
> The preceding statement is not true on Microsoft Windows: there, any
> changes in the `pg_hba.conf` file are immediately applied by
> subsequent new connections.

The system view [pg\_hba\_file\_rules](#view-pg-hba-file-rules) can be
helpful for pre-testing changes to the `pg_hba.conf` file, or for
diagnosing problems if loading of the file did not have the desired
effects. Rows in the view with non-null error fields indicate problems
in the corresponding lines of the file.

> **Tip**
>
> 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
[example\_title](#example-pg-hba.conf). See the next section for details
on the different authentication methods.

    # 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        scram-sha-256

    # Allow any user from hosts in the example.com domain to connect to
    # any database if the user's password is correctly supplied.
    #
    # Require SCRAM authentication for most users, but make an exception
    # for user 'mike', who uses an older client that doesn't support SCRAM
    # authentication.
    #
    # TYPE  DATABASE        USER            ADDRESS                 METHOD
    host    all             mike            .example.com            md5
    host    all             all             .example.com            scram-sha-256

    # In the absence of preceding "host" lines, these three lines will
    # reject all connections from 192.168.54.1 (since that entry will be
    # matched first), but allow GSSAPI-encrypted 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.  Unencrypted GSSAPI connections
    # (which "fall through" to the third line since "hostgssenc" only matches
    # encrypted GSSAPI connections) are allowed, but only from 192.168.12.10.
    #
    # TYPE  DATABASE        USER            ADDRESS                 METHOD
    host    all             all             192.168.54.1/32         reject
    hostgssenc all          all             0.0.0.0/0               gss
    host    all             all             192.168.12.10/32        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 {#auth-username-maps}
==============

User name maps

When using an external authentication system such as Ident or GSSAPI,
the name of the operating system user that initiated the connection
might not be the same as the database user (role) that is to be used. 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.conf`pg\_ident.conf and is stored in the cluster\'s data
directory. (It is possible to place the map file elsewhere, however; see
the [???](#guc-ident-file) configuration parameter.) The ident map file
contains lines of the general form: map-name system-username
database-username Comments, whitespace and line continuations 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
[???](#posix-syntax-details) 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`.

> **Tip**
>
> 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`, calling the SQL function `pg_reload_conf()`, or using
`kill
   -HUP`) to make it re-read the file.

The system view
[pg\_ident\_file\_mappings](#view-pg-ident-file-mappings) can be helpful
for pre-testing changes to the `pg_ident.conf` file, or for diagnosing
problems if loading of the file did not have the desired effects. Rows
in the view with non-null error fields indicate problems in the
corresponding lines of the file.

A `pg_ident.conf` file that could be used in conjunction with the
`pg_hba.conf` file in [example\_title](#example-pg-hba.conf) is shown in
[example\_title](#example-pg-ident.conf). 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`.

    # 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 {#auth-methods}
======================

PostgreSQL provides various methods for authenticating users:

-   [Trust authentication](#auth-trust), which simply trusts that users
    are who they say they are.

-   [Password authentication](#auth-password), which requires that users
    send a password.

-   [GSSAPI authentication](#gssapi-auth), which relies on a
    GSSAPI-compatible security library. Typically this is used to access
    an authentication server such as a Kerberos or Microsoft Active
    Directory server.

-   [SSPI authentication](#sspi-auth), which uses a Windows-specific
    protocol similar to GSSAPI.

-   [Ident authentication](#auth-ident), which relies on an
    "Identification Protocol" ([RFC
    1413](https://tools.ietf.org/html/rfc1413)) service on the client\'s
    machine. (On local Unix-socket connections, this is treated as peer
    authentication.)

-   [Peer authentication](#auth-peer), which relies on operating system
    facilities to identify the process at the other end of a local
    connection. This is not supported for remote connections.

-   [LDAP authentication](#auth-ldap), which relies on an LDAP
    authentication server.

-   [RADIUS authentication](#auth-radius), which relies on a RADIUS
    authentication server.

-   [Certificate authentication](#auth-cert), which requires an SSL
    connection and authenticates users by checking the SSL certificate
    they send.

-   [PAM authentication](#auth-pam), which relies on a PAM (Pluggable
    Authentication Modules) library.

-   [BSD authentication](#auth-bsd), which relies on the BSD
    Authentication framework (currently available only on OpenBSD).

Peer authentication is usually recommendable for local connections,
though trust authentication might be sufficient in some circumstances.
Password authentication is the easiest choice for remote connections.
All the other options require some kind of external security
infrastructure (usually an authentication server or a certificate
authority for issuing SSL certificates), or are platform-specific.

The following sections describe each of these authentication methods in
more detail.

Trust Authentication {#auth-trust}
====================

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
[???](#runtime-config-connection). 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 {#auth-password}
=======================

MD5

SCRAM

password

authentication

There are several password-based authentication methods. These methods
operate similarly but differ in how the users\' passwords are stored on
the server and how the password provided by a client is sent across the
connection.

`scram-sha-256`

:   The method `scram-sha-256` performs SCRAM-SHA-256 authentication, as
    described in [RFC 7677](https://tools.ietf.org/html/rfc7677). It is
    a challenge-response scheme that prevents password sniffing on
    untrusted connections and supports storing passwords on the server
    in a cryptographically hashed form that is thought to be secure.

    This is the most secure of the currently provided methods, but it is
    not supported by older client libraries.

`md5`

:   The method `md5` uses a custom less secure challenge-response
    mechanism. It prevents password sniffing and avoids storing
    passwords on the server in plain text but provides no protection if
    an attacker manages to steal the password hash from the server.
    Also, the MD5 hash algorithm is nowadays no longer considered secure
    against determined attacks.

    The `md5` method cannot be used with the
    [???](#guc-db-user-namespace) feature.

    To ease transition from the `md5` method to the newer SCRAM method,
    if `md5` is specified as a method in `pg_hba.conf` but the user\'s
    password on the server is encrypted for SCRAM (see below), then
    SCRAM-based authentication will automatically be chosen instead.

`password`

:   The method `password` sends the password in clear-text and is
    therefore vulnerable to password "sniffing" attacks. It should
    always be avoided if possible. If the connection is protected by SSL
    encryption then `password` can be used safely, though. (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 [???](#sql-createrole) and [???](#sql-alterrole), e.g.,
`CREATE ROLE foo WITH LOGIN PASSWORD 'secret'`, or the psql command
`\password`. If no password has been set up for a user, the stored
password is null and password authentication will always fail for that
user.

The availability of the different password-based authentication methods
depends on how a user\'s password on the server is encrypted (or hashed,
more accurately). This is controlled by the configuration parameter
[???](#guc-password-encryption) at the time the password is set. If a
password was encrypted using the `scram-sha-256` setting, then it can be
used for the authentication methods `scram-sha-256` and `password` (but
password transmission will be in plain text in the latter case). The
authentication method specification `md5` will automatically switch to
using the `scram-sha-256` method in this case, as explained above, so it
will also work. If a password was encrypted using the `md5` setting,
then it can be used only for the `md5` and `password` authentication
method specifications (again, with the password transmitted in plain
text in the latter case). (Previous PostgreSQL releases supported
storing the password on the server in plain text. This is no longer
possible.) To check the currently stored password hashes, see the system
catalog `pg_authid`.

To upgrade an existing installation from `md5` to `scram-sha-256`, after
having ensured that all client libraries in use are new enough to
support SCRAM, set `password_encryption = 'scram-sha-256'` in
`postgresql.conf`, make all users set new passwords, and change the
authentication method specifications in `pg_hba.conf` to
`scram-sha-256`.

GSSAPI Authentication {#gssapi-auth}
=====================

GSSAPI

GSSAPI is an industry-standard protocol for secure authentication
defined in [RFC 2743](https://tools.ietf.org/html/rfc2743). PostgreSQL
supports GSSAPI for authentication, communications encryption, or both.
GSSAPI provides automatic authentication (single sign-on) for systems
that support it. The authentication itself is secure. If GSSAPI
encryption or SSL encryption is used, the data sent along the database
connection will be encrypted; otherwise, it will not.

GSSAPI support has to be enabled when PostgreSQL is built; see
[???](#installation) for more information.

When GSSAPI uses Kerberos, it uses a standard service principal
(authentication identity) name in the format
`servicename/hostname@realm`. The principal name used by a particular
installation is not encoded in the PostgreSQL server in any way; rather
it is specified in the keytab file that the server reads to determine
its identity. If multiple principals are listed in the keytab file, the
server will accept any one of them. The server\'s realm name is the
preferred realm specified in the Kerberos configuration file(s)
accessible to the server.

When connecting, the client must know the principal name of the server
it intends to connect to. The servicename part of the principal is
ordinarily `postgres`, but another value can be selected via libpq\'s
[???](#libpq-connect-krbsrvname) connection parameter. The hostname part
is the fully qualified host name that libpq is told to connect to. The
realm name is the preferred realm specified in the Kerberos
configuration file(s) accessible to the client.

The client will also have a principal name for its own identity (and it
must have a valid ticket for this principal). To use GSSAPI for
authentication, the client principal must be associated with a
PostgreSQL database user name. The `pg_ident.conf` configuration file
can be used to map principals to user names; for example,
`pgusername@realm` could be mapped to just `pgusername`. Alternatively,
you can use the full `username@realm` principal as the role name in
PostgreSQL without any mapping.

PostgreSQL also supports mapping client principals to user names by just
stripping the realm from the principal. This method is supported for
backwards compatibility and is strongly discouraged as it is then
impossible to distinguish different users with the same user name but
coming from different realms. To enable this, set `include_realm` to 0.
For simple single-realm installations, doing that combined with setting
the `krb_realm` parameter (which checks that the principal\'s realm
matches exactly what is in the `krb_realm` parameter) is still secure;
but this is a less capable approach compared to specifying an explicit
mapping in `pg_ident.conf`.

The location of the server\'s keytab file is specified by the
[???](#guc-krb-server-keyfile) configuration parameter. For security
reasons, it is recommended to use a separate keytab just for the
PostgreSQL server rather than allowing the server to read the system
keytab file. Make sure that your server keytab file is readable (and
preferably only readable, not writable) by the PostgreSQL server
account. (See also [???](#postgres-user).)

The keytab file is generated using the Kerberos software; see the
Kerberos documentation for details. The following example shows doing
this using the kadmin tool of MIT-compatible Kerberos 5 implementations:

    kadmin% addprinc -randkey postgres/server.my.domain.org
    kadmin% ktadd -k krb5.keytab postgres/server.my.domain.org

The following authentication options are supported for the GSSAPI
authentication method:

`include_realm`

:   If set to 0, the realm name from the authenticated user principal is
    stripped off before being passed through the user name mapping
    ([User Name Maps](#auth-username-maps)). This is discouraged and is
    primarily available for backwards compatibility, as it is not secure
    in multi-realm environments unless `krb_realm` is also used. It is
    recommended to leave `include_realm` set to the default (1) and to
    provide an explicit mapping in `pg_ident.conf` to convert principal
    names to PostgreSQL user names.

`map`

:   Allows mapping from client principals to database user names. See
    [User Name Maps](#auth-username-maps) for details. For a
    GSSAPI/Kerberos principal, such as `username@EXAMPLE.COM` (or, less
    commonly, `username/hostbased@EXAMPLE.COM`), the user name used for
    mapping is `username@EXAMPLE.COM` (or
    `username/hostbased@EXAMPLE.COM`, respectively), unless
    `include_realm` has been set to 0, in which case `username` (or
    `username/hostbased`) is what is seen as the system user name 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.

In addition to these settings, which can be different for different
`pg_hba.conf` entries, there is the server-wide
[???](#guc-krb-caseins-users) configuration parameter. If that is set to
true, client principals are matched to user map entries
case-insensitively. `krb_realm`, if set, is also matched
case-insensitively.

SSPI Authentication {#sspi-auth}
===================

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 [GSSAPI Authentication](#gssapi-auth) for details.

The following configuration options are supported for SSPI:

`include_realm`

:   If set to 0, the realm name from the authenticated user principal is
    stripped off before being passed through the user name mapping
    ([User Name Maps](#auth-username-maps)). This is discouraged and is
    primarily available for backwards compatibility, as it is not secure
    in multi-realm environments unless `krb_realm` is also used. It is
    recommended to leave `include_realm` set to the default (1) and to
    provide an explicit mapping in `pg_ident.conf` to convert principal
    names to PostgreSQL user names.

`compat_realm`

:   If set to 1, the domain\'s SAM-compatible name (also known as the
    NetBIOS name) is used for the `include_realm` option. This is the
    default. If set to 0, the true realm name from the Kerberos user
    principal name is used.

    Do not disable this option unless your server runs under a domain
    account (this includes virtual service accounts on a domain member
    system) and all clients authenticating through SSPI are also using
    domain accounts, or authentication will fail.

`upn_username`

:   If this option is enabled along with `compat_realm`, the user name
    from the Kerberos UPN is used for authentication. If it is disabled
    (the default), the SAM-compatible user name is used. By default,
    these two names are identical for new user accounts.

    Note that libpq uses the SAM-compatible name if no explicit user
    name is specified. If you use libpq or a driver based on it, you
    should leave this option disabled or explicitly specify user name in
    the connection string.

`map`

:   Allows for mapping between system and database user names. See [User
    Name Maps](#auth-username-maps) for details. For an SSPI/Kerberos
    principal, such as `username@EXAMPLE.COM` (or, less commonly,
    `username/hostbased@EXAMPLE.COM`), the user name used for mapping is
    `username@EXAMPLE.COM` (or `username/hostbased@EXAMPLE.COM`,
    respectively), unless `include_realm` has been set to 0, in which
    case `username` (or `username/hostbased`) is what is seen as the
    system user name 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 {#auth-ident}
====================

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.

> **Note**
>
> When ident is specified for a local (non-TCP/IP) connection, peer
> authentication (see [Peer Authentication](#auth-peer)) will be used
> instead.

The following configuration options are supported for ident:

`map`

:   Allows for mapping between system and database user names. See [User
    Name Maps](#auth-username-maps) for details.

The "Identification Protocol" is described in [RFC
1413](https://tools.ietf.org/html/rfc1413). 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 they choose. 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.

Peer Authentication {#auth-peer}
===================

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 [User
    Name Maps](#auth-username-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
macOS, and Solaris.

LDAP Authentication {#auth-ldap}
===================

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.

`ldapscheme`

:   Set to `ldaps` to use LDAPS. This is a non-standard way of using
    LDAP over SSL, supported by some LDAP server implementations. See
    also the `ldaptls` option for an alternative.

`ldaptls`

:   Set to 1 to make the connection between PostgreSQL and the LDAP
    server use TLS encryption. This uses the `StartTLS` operation per
    [RFC 4513](https://tools.ietf.org/html/rfc4513). See also the
    `ldapscheme` option for an alternative.

Note that using `ldapscheme` or `ldaptls` only encrypts the traffic
between the PostgreSQL server and the LDAP server. The connection
between the PostgreSQL server and the PostgreSQL client will still be
unencrypted unless SSL is used there as well.

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.

`ldapsearchfilter`

:   The search filter to use when doing search+bind authentication.
    Occurrences of `$username` will be replaced with the user name. This
    allows for more flexible search filters than `ldapsearchattribute`.

`ldapurl`

:   An [RFC 4516](https://tools.ietf.org/html/rfc4516) 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\[s\]://host\[:port\]/basedn\[?\[attribute\]\[?\[scope\]\[?\[filter\]\]\]\]
    scope must be one of `base`, `one`, `sub`, typically the last. (The
    default is `base`, which is normally not useful in this
    application.) attribute can nominate a single attribute, in which
    case it is used as a value for `ldapsearchattribute`. If attribute
    is empty then filter can be used as a value for `ldapsearchfilter`.

    The URL scheme `ldaps` chooses the LDAPS method for making LDAP
    connections over SSL, equivalent to using `ldapscheme=ldaps`. To use
    encrypted LDAP connections using the `StartTLS` operation, use the
    normal URL scheme `ldap` and specify the `ldaptls` option in
    addition to `ldapurl`.

    For non-anonymous binds, `ldapbinddn` and `ldapbindpasswd` must be
    specified as separate options.

    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.

When using search+bind mode, the search can be performed using a single
attribute specified with `ldapsearchattribute`, or using a custom search
filter specified with `ldapsearchfilter`. Specifying
`ldapsearchattribute=foo` is equivalent to specifying
`ldapsearchfilter="(foo=$username)"`. If neither option is specified the
default is `ldapsearchattribute=uid`.

If PostgreSQL was compiled with OpenLDAP as the LDAP client library, the
`ldapserver` setting may be omitted. In that case, a list of host names
and ports is looked up via [RFC
2782](https://tools.ietf.org/html/rfc2782) DNS SRV records. The name
`_ldap._tcp.DOMAIN` is looked up, where `DOMAIN` is extracted from
`ldapbasedn`.

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.

Here is an example for a search+bind configuration that uses
`ldapsearchfilter` instead of `ldapsearchattribute` to allow
authentication by user ID or email address:

    host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchfilter="(|(uid=$username)(mail=$username))"

Here is an example for a search+bind configuration that uses DNS SRV
discovery to find the host name(s) and port(s) for the LDAP service for
the domain name `example.net`:

    host ... ldap ldapbasedn="dc=example,dc=net"

> **Tip**
>
> 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 {#auth-radius}
=====================

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
request with either `Access Accept` or `Access Reject`. There is no
support for RADIUS accounting.

Multiple RADIUS servers can be specified, in which case they will be
tried sequentially. If a negative response is received from a server,
the authentication will fail. If no response is received, the next
server in the list will be tried. To specify multiple servers, separate
the server names with commas and surround the list with double quotes.
If multiple servers are specified, the other RADIUS options can also be
given as comma-separated lists, to provide individual values for each
server. They can also be specified as a single value, in which case that
value will apply to all servers.

The following configuration options are supported for RADIUS:

`radiusservers`

:   The DNS names or IP addresses of the RADIUS servers to connect to.
    This parameter is required.

`radiussecrets`

:   The shared secrets used when talking securely to the RADIUS servers.
    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.

    > **Note**
    >
    > 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.

`radiusports`

:   The port numbers to connect to on the RADIUS servers. If no port is
    specified, the default RADIUS port (`1812`) will be used.

`radiusidentifiers`

:   The strings to be used as `NAS Identifier` in the RADIUS requests.
    This parameter can be used, for example, to identify which database
    cluster the user is attempting to connect to, which can be useful
    for policy matching on the RADIUS server. If no identifier is
    specified, the default `postgresql` will be used.

If it is necessary to have a comma or whitespace in a RADIUS parameter
value, that can be done by putting double quotes around the value, but
it is tedious because two layers of double-quoting are now required. An
example of putting whitespace into RADIUS secret strings is:

    host ... radius radiusservers="server1,server2" radiussecrets="""secret one"",""secret two"""

Certificate Authentication {#auth-cert}
==========================

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, trusted 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 [User
    Name Maps](#auth-username-maps) for details.

It is redundant to use the `clientcert` option with `cert`
authentication because `cert` authentication is effectively `trust`
authentication with `clientcert=verify-full`.

PAM Authentication {#auth-pam}
==================

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 and optionally the connected
remote host name or IP address. 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](https://www.kernel.org/pub/linux/libs/pam/).

The following configuration options are supported for PAM:

`pamservice`

:   PAM service name.

`pam_use_hostname`

:   Determines whether the remote IP address or the host name is
    provided to PAM modules through the `PAM_RHOST` item. By default,
    the IP address is used. Set this option to 1 to use the resolved
    host name instead. Host name resolution can lead to login delays.
    (Most PAM configurations don\'t use this information, so it is only
    necessary to consider this setting if a PAM configuration was
    specifically created to make use of it.)

> **Note**
>
> 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.

BSD Authentication {#auth-bsd}
==================

BSD Authentication

This authentication method operates similarly to `password` except that
it uses BSD Authentication to verify the password. BSD Authentication is
used only to validate user name/password pairs. Therefore the user\'s
role must already exist in the database before BSD Authentication can be
used for authentication. The BSD Authentication framework is currently
only available on OpenBSD.

BSD Authentication in PostgreSQL uses the `auth-postgresql` login type
and authenticates with the `postgresql` login class if that\'s defined
in `login.conf`. By default that login class does not exist, and
PostgreSQL will use the default login class.

> **Note**
>
> To use BSD Authentication, the PostgreSQL user account (that is, the
> operating system user running the server) must first be added to the
> `auth` group. The `auth` group exists by default on OpenBSD systems.

Authentication Problems {#client-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.

> **Tip**
>
> 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.
