The following subsections describe the authentication methods in more detail.
    When trust authentication is specified,
    PostgreSQL assumes that anyone who can
    connect to the server is authorized to access the database with
    whatever database user name they specify (even superuser names).
    Of course, restrictions made in the database and
    user columns still apply.
    This method should only be used when there is adequate
    operating-system-level protection on connections to the server.
   
    trust authentication is appropriate and very
    convenient for local connections on a single-user workstation.  It
    is usually not appropriate by itself on a multiuser
    machine.  However, you might be able to use trust even
    on a multiuser machine, if you restrict access to the server's
    Unix-domain socket file using file-system permissions.  To do this, set the
    unix_socket_permissions (and possibly
    unix_socket_group) configuration parameters as
    described in Section 19.3.  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).
   
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.  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 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
    CREATE USER and
    ALTER ROLE,
    e.g., CREATE USER foo WITH 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 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 is an industry-standard protocol for secure authentication defined in RFC 2743. PostgreSQL supports GSSAPI with Kerberos authentication according to RFC 1964. GSSAPI provides automatic authentication (single sign-on) for systems that support it. The authentication itself is secure, but the data sent over the database connection will be sent unencrypted unless SSL is used.
GSSAPI support has to be enabled when PostgreSQL is built; see Chapter 16 for more information.
    When GSSAPI uses
    Kerberos, it uses a standard principal
    in the format
    servicename/hostname@realmkrbsrvname connection parameter. (See
    also Section 33.1.2.) 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 can be mapped to different PostgreSQL
    database user names with pg_ident.conf.  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 a parameter to strip 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.
   
    Make sure that your server keytab file is readable (and preferably
    only readable, not writable) by the PostgreSQL
    server account.  (See also Section 18.1.) The location
    of the key file is specified by the krb_server_keyfile configuration
    parameter. The default is
    /usr/local/pgsql/etc/krb5.keytab (or whatever
    directory was specified as sysconfdir at build time).
    For security reasons, it is recommended to use a separate keytab
    just for the PostgreSQL server rather
    than opening up permissions on the system keytab file.
   
The keytab file is generated by the Kerberos software; see the Kerberos documentation for details. The following example is for MIT-compatible Kerberos 5 implementations:
kadmin%ank -randkey postgres/server.my.domain.orgkadmin%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 Section 20.2.
   
The following configuration options are supported for GSSAPI:
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
        (Section 20.2). 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 for mapping between system and database user names. See
        Section 20.2 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_realmSets the realm to match user principal names against. If this parameter is set, only users of that realm will be accepted. If it is not set, users of any realm can connect, subject to whatever user name mapping is done.
    SSPI is a Windows
    technology for secure authentication with single sign-on.
    PostgreSQL will use SSPI in
    negotiate mode, which will use
    Kerberos when possible and automatically
    fall back to NTLM in other cases.
    SSPI authentication only works when both
    server and client are running Windows,
    or, on non-Windows platforms, when GSSAPI
    is available.
   
When using Kerberos authentication, SSPI works the same way GSSAPI does; see Section 20.3.3 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
        (Section 20.2). 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
        Section 20.2 for details.  For a 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_realmSets the realm to match user principal names against. If this parameter is set, only users of that realm will be accepted. If it is not set, users of any realm can connect, subject to whatever user name mapping is done.
The ident authentication method works by obtaining the client's operating system user name from an ident server and using it as the allowed database user name (with an optional user name mapping). This is only supported on TCP/IP connections.
When ident is specified for a local (non-TCP/IP) connection, peer authentication (see Section 20.3.6) will be used instead.
The following configuration options are supported for ident:
mapAllows for mapping between system and database user names. See Section 20.2 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 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.
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:
mapAllows for mapping between system and database user names. See Section 20.2 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.
   
    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:
ldapserverNames or IP addresses of LDAP servers to connect to. Multiple servers may be specified, separated by spaces.
ldapportPort number on LDAP server to connect to. If no port is specified, the LDAP library's default port setting will be used.
ldaptlsSet 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:
ldapprefixString to prepend to the user name when forming the DN to bind as, when doing simple bind authentication.
ldapsuffixString 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:
ldapbasednRoot DN to begin the search for the user in, when doing search+bind authentication.
ldapbinddnDN of user to bind to the directory with to perform the search when doing search+bind authentication.
ldapbindpasswdPassword 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.
        
ldapurlAn 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.
    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:
radiusserversThe DNS names or IP addresses of the RADIUS servers to connect to. This parameter is required.
radiussecretsThe 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.
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"""
    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:
mapAllows for mapping between system and database user names. See Section 20.2 for details.
    In a pg_hba.conf record specifying certificate
    authentication, the authentication option clientcert is
    assumed to be 1, and it cannot be turned off since a client
    certificate is necessary for this method.  What the cert
    method adds to the basic clientcert certificate validity test
    is a check that the cn attribute matches the database
    user name.
   
    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.
   
The following configuration options are supported for PAM:
pamservicePAM 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.)
       
     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.
    
    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.
   
     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.