<!-- $PostgreSQL: pgsql/doc/src/sgml/client-auth.sgml,v 1.124 2009/10/01 01:58:57 tgl Exp $ -->

<chapter id="client-authentication">
 <title>Client Authentication</title>

 <indexterm zone="client-authentication">
  <primary>client authentication</primary>
 </indexterm>

 <para>
  When a client application connects to the database server, it
  specifies which <productname>PostgreSQL</productname> 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
  <xref linkend="user-manag"> for more information. Therefore, it is
  essential to restrict which database users can connect.
 </para>

 <note>
  <para>
   As explained in <xref linkend="user-manag">,
   <productname>PostgreSQL</productname> actually does privilege
   management in terms of <quote>roles</>.  In this chapter, we
   consistently use <firstterm>database user</> to mean <quote>role with the
   <literal>LOGIN</> privilege</quote>.
  </para>
 </note>

 <para>
  <firstterm>Authentication</firstterm> 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.
 </para>

 <para>
  <productname>PostgreSQL</productname> 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.
 </para>

 <para>
  <productname>PostgreSQL</productname> 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.
 </para>

 <sect1 id="auth-pg-hba-conf">
  <title>The <filename>pg_hba.conf</filename> file</title>

  <indexterm zone="auth-pg-hba-conf">
   <primary>pg_hba.conf</primary>
  </indexterm>

  <para>
   Client authentication is controlled by a configuration file,
   which traditionally is named
   <filename>pg_hba.conf</filename> and is stored in the database
   cluster's data directory.
   (<acronym>HBA</> stands for host-based authentication.) A default
   <filename>pg_hba.conf</filename> file is installed when the data
   directory is initialized by <command>initdb</command>.  It is
   possible to place the authentication configuration file elsewhere,
   however; see the <xref linkend="guc-hba-file"> configuration parameter.
  </para>

  <para>
   The general format of the <filename>pg_hba.conf</filename> file is
   a set of records, one per line. Blank lines are ignored, as is any
   text after the <literal>#</literal> comment character. 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 quoted. Records
   cannot be continued across lines.
  </para>

  <para>
   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 <quote>fall-through</> or
   <quote>backup</>: if one record is chosen and the authentication
   fails, subsequent records are not considered. If no record matches,
   access is denied.
  </para>

  <para>
   A record can have one of the seven formats
<synopsis>
local      <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
host       <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
hostssl    <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
host       <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
hostssl    <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
</synopsis>
   The meaning of the fields is as follows:

   <variablelist>
    <varlistentry>
     <term><literal>local</literal></term>
     <listitem>
      <para>
       This record matches connection attempts using Unix-domain
       sockets.  Without a record of this type, Unix-domain socket
       connections are disallowed.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>host</literal></term>
     <listitem>
      <para>
       This record matches connection attempts made using TCP/IP.
       <literal>host</literal> records match either
       <acronym>SSL</acronym> or non-<acronym>SSL</acronym> connection
       attempts.
      </para>
     <note>
      <para>
       Remote TCP/IP connections will not be possible unless
       the server is started with an appropriate value for the
       <xref linkend="guc-listen-addresses"> configuration parameter,
       since the default behavior is to listen for TCP/IP connections
       only on the local loopback address <literal>localhost</>.
      </para>
     </note>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>hostssl</literal></term>
     <listitem>
      <para>
       This record matches connection attempts made using TCP/IP,
       but only when the connection is made with <acronym>SSL</acronym>
       encryption.
      </para>

      <para>
       To make use of this option the server must be built with
       <acronym>SSL</acronym> support. Furthermore,
       <acronym>SSL</acronym> must be enabled at server start time
       by setting the <xref linkend="guc-ssl"> configuration parameter (see
       <xref linkend="ssl-tcp"> for more information).
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>hostnossl</literal></term>
     <listitem>
      <para>
       This record type has the opposite logic to <literal>hostssl</>:
       it only matches connection attempts made over
       TCP/IP that do not use <acronym>SSL</acronym>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>database</replaceable></term>
     <listitem>
      <para>
       Specifies which database name(s) this record matches.  The value
       <literal>all</literal> specifies that it matches all databases.
       The value <literal>sameuser</> specifies that the record
       matches if the requested database has the same name as the
       requested user.  The value <literal>samerole</> specifies that
       the requested user must be a member of the role with the same
       name as the requested database.  (<literal>samegroup</> is an
       obsolete but still accepted spelling of <literal>samerole</>.)
       Otherwise, this is the name of
       a specific <productname>PostgreSQL</productname> 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 <literal>@</>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>user</replaceable></term>
     <listitem>
      <para>
       Specifies which database user name(s) this record
       matches. The value <literal>all</literal> specifies that it
       matches all users.  Otherwise, this is either the name of a specific
       database user, or a group name preceded by <literal>+</>.
       (Recall that there is no real distinction between users and groups
       in <productname>PostgreSQL</>; a <literal>+</> mark really means
       <quote>match any of the roles that are directly or indirectly members
       of this role</>, while a name without a <literal>+</> mark matches
       only that specific role.)
       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 <literal>@</>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>CIDR-address</replaceable></term>
     <listitem>
      <para>
       Specifies the client machine IP address range that this record
       matches. This field contains an IP address in standard dotted decimal
       notation and a CIDR mask length. (IP addresses can only be
       specified numerically, not as domain or host names.)  The mask
       length indicates the number of high-order bits of the client
       IP address that must match.  Bits to the right of this must
       be zero in the given IP address.
       There must not be any white space between the IP address, the
       <literal>/</literal>, and the CIDR mask length.
      </para>

      <para>
       Instead of a <replaceable>CIDR-address</replaceable>, you can write
       <literal>samehost</literal> to match any of the server's own IP
       addresses, or <literal>samenet</literal> to match any address in any
       subnet that the server is directly connected to.
      </para>

      <para>
       Typical examples of a <replaceable>CIDR-address</replaceable> are
       <literal>172.20.143.89/32</literal> for a single host, or
       <literal>172.20.143.0/24</literal> for a small network, or
       <literal>10.6.0.0/16</literal> for a larger one.
       To specify a single host, use a CIDR mask of 32 for IPv4 or
       128 for IPv6.  In a network address, do not omit trailing zeroes.
      </para>

      <para>
       An IP address given in IPv4 format will match IPv6 connections that
       have the corresponding address, for example <literal>127.0.0.1</>
       will match the IPv6 address <literal>::ffff:127.0.0.1</>.  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.
      </para>

      <para>
       This field only applies to <literal>host</literal>,
       <literal>hostssl</literal>, and <literal>hostnossl</> records.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>IP-address</replaceable></term>
     <term><replaceable>IP-mask</replaceable></term>
     <listitem>
      <para>
       These fields can be used as an alternative to the
       <replaceable>CIDR-address</replaceable> notation. Instead of
       specifying the mask length, the actual mask is specified in a
       separate column. For example, <literal>255.0.0.0</> represents an IPv4
       CIDR mask length of 8, and <literal>255.255.255.255</> represents a
       CIDR mask length of 32.
      </para>

      <para>
       These fields only apply to <literal>host</literal>,
       <literal>hostssl</literal>, and <literal>hostnossl</> records.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>auth-method</replaceable></term>
     <listitem>
      <para>
       Specifies the authentication method to use when a connection matches
       this record. The possible choices are summarized here; details
       are in <xref linkend="auth-methods">.

       <variablelist>
        <varlistentry>
         <term><literal>trust</></term>
         <listitem>
         <para>
          Allow the connection unconditionally. This method
          allows anyone that can connect to the
          <productname>PostgreSQL</productname> database server to login as
          any <productname>PostgreSQL</productname> user they like,
          without the need for a password.  See <xref
          linkend="auth-trust"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>reject</></term>
        <listitem>
         <para>
          Reject the connection unconditionally. This is useful for
          <quote>filtering out</> certain hosts from a group.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>md5</></term>
        <listitem>
         <para>
          Require the client to supply an MD5-encrypted password for
          authentication.
          See <xref linkend="auth-password"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>password</></term>
        <listitem>
         <para>
          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 <xref linkend="auth-password"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>gss</></term>
        <listitem>
         <para>
          Use GSSAPI to authenticate the user. This is only
          available for TCP/IP connections. See <xref
          linkend="gssapi-auth"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>sspi</></term>
        <listitem>
         <para>
          Use SSPI to authenticate the user. This is only
          available on Windows. See <xref
          linkend="sspi-auth"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>krb5</></term>
        <listitem>
         <para>
          Use Kerberos V5 to authenticate the user. This is only
          available for TCP/IP connections.  See <xref
          linkend="kerberos-auth"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>ident</></term>
        <listitem>
         <para>
          Obtain the operating system user name of the client (for
          TCP/IP connections by contacting the ident server on the
          client, for local connections by getting it from the
          operating system) and check if it matches the requested
          database user name.
          See <xref linkend="auth-ident"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>ldap</></term>
        <listitem>
         <para>
          Authenticate using an LDAP server. See <xref
          linkend="auth-ldap"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>cert</></term>
        <listitem>
         <para>
          Authenticate using SSL client certificates. See
          <xref linkend="auth-cert"> for details.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>pam</></term>
        <listitem>
         <para>
          Authenticate using the Pluggable Authentication Modules
          (PAM) service provided by the operating system.  See <xref
          linkend="auth-pam"> for details.
         </para>
        </listitem>
       </varlistentry>
      </variablelist>

      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>auth-options</replaceable></term>
     <listitem>
      <para>
       After the <replaceable>auth-method</> field, there can be field(s) of
       the form <replaceable>name</><literal>=</><replaceable>value</> that
       specify options for the authentication method. Details about which
       options are available for which authentication method appear below.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   Files included by <literal>@</> constructs are read as lists of names,
   which can be separated by either whitespace or commas.  Comments are
   introduced by <literal>#</literal>, just as in
   <filename>pg_hba.conf</filename>, and nested <literal>@</> constructs are
   allowed.  Unless the file name following <literal>@</> is an absolute
   path, it is taken to be relative to the directory containing the
   referencing file.
  </para>

  <para>
   Since the <filename>pg_hba.conf</filename> 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 <literal>trust</>
   authentication for local TCP/IP connections but require a password for
   remote TCP/IP connections. In this case a record specifying
   <literal>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.
  </para>

  <para>
   The <filename>pg_hba.conf</filename> file is read on start-up and when
   the main server process receives a
   <systemitem>SIGHUP</systemitem><indexterm><primary>SIGHUP</primary></indexterm>
   signal. If you edit the file on an
   active system, you will need to signal the server
   (using <literal>pg_ctl reload</> or <literal>kill -HUP</>) to make it
   re-read the file.
  </para>

  <tip>
   <para>
    To connect to a particular database, a user must not only pass the
    <filename>pg_hba.conf</filename> checks, but must have the
    <literal>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 <literal>CONNECT</> privilege
    than to put the rules into <filename>pg_hba.conf</filename> entries.
   </para>
  </tip>

  <para>
   Some examples of <filename>pg_hba.conf</filename> entries are shown in
   <xref linkend="example-pg-hba.conf">. See the next section for details on the
   different authentication methods.
  </para>

   <example id="example-pg-hba.conf">
    <title>Example <filename>pg_hba.conf</filename> entries</title>
<programlisting>
# Allow any user on the local system to connect to any database under
# any database user name using Unix-domain sockets (the default for local
# connections).
#
# TYPE  DATABASE    USER        CIDR-ADDRESS          METHOD
local   all         all                               trust

# The same using local loopback TCP/IP connections.
#
# TYPE  DATABASE    USER        CIDR-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

# 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 Unix user name).
#
# TYPE  DATABASE    USER        CIDR-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        CIDR-ADDRESS          METHOD
host    postgres    all         192.168.12.10/32      md5

# In the absence of preceding "host" lines, these two lines will
# reject all connections from 192.168.54.1 (since that entry will be
# matched first), but allow Kerberos 5 connections from anywhere else
# on the Internet.  The zero mask means that no bits of the host IP
# address are considered so it matches any host.
#
# TYPE  DATABASE    USER        CIDR-ADDRESS          METHOD
host    all         all         192.168.54.1/32       reject
host    all         all         0.0.0.0/0             krb5

# 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        CIDR-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        CIDR-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
</programlisting>
   </example>
 </sect1>

 <sect1 id="auth-username-maps">
  <title>Username maps</title>

  <indexterm zone="auth-username-maps">
   <primary>Username maps</primary>
  </indexterm>

  <para>
   When using an external authentication system like Ident or GSSAPI,
   the name of the operating system user that initiated the connection
   might not be the same as the database user he needs to connect as.
   In this case, a user name map can be applied to map the operating system
   username to a database user.  To use username mapping, specify
   <literal>map</literal>=<replaceable>map-name</replaceable>
   in the options field in <filename>pg_hba.conf</filename>. This option is
   supported for all authentication methods that receive external usernames.
   Since different mappings might be needed for different connections,
   the name of the map to be used is specified in the
   <replaceable>map-name</replaceable> parameter in <filename>pg_hba.conf</filename>
   to indicate which map to use for each individual connection.
  </para>

  <para>
   Username maps are defined in the ident map file, which by default is named
   <filename>pg_ident.conf</><indexterm><primary>pg_ident.conf</primary></indexterm>
   and is stored in the
   cluster's data directory.  (It is possible to place the map file
   elsewhere, however; see the <xref linkend="guc-ident-file">
   configuration parameter.)
   The ident map file contains lines of the general form:
<synopsis>
<replaceable>map-name</> <replaceable>system-username</> <replaceable>database-username</>
</synopsis>
   Comments and whitespace are handled in the same way as in
   <filename>pg_hba.conf</>.  The
   <replaceable>map-name</> is an arbitrary name that will be used to
   refer to this mapping in <filename>pg_hba.conf</filename>. The other
   two fields specify an operating system user name and a matching
   database user name. The same <replaceable>map-name</> can be
   used repeatedly to specify multiple user-mappings within a single map.
  </para>
  <para>
   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 <quote>this operating system
   user is allowed to connect as this database user</quote>, rather than
   implying that they are equivalent.  The connection will be allowed if
   there is any map entry that matches the user name obtained from the
   external authentication system to the database user name that the
   user has requested to connect as.
  </para>
  <para>
   If the <replaceable>system-username</> field starts with a slash (<literal>/</>),
   the remainder of the field is treated as a regular expression.
   (See <xref linkend="posix-syntax-details"> for details of
   <productname>PostgreSQL</>'s regular expression syntax.
   Regular expressions in username maps are always treated as being
   <quote>advanced</> flavor.)  The regular
   expression can include a single capture, or parenthesized subexpression,
   which can then be referenced in the <replaceable>database-username</>
   field as <literal>\1</> (backslash-one).  This allows the mapping of
   multiple usernames in a single line, which is particularly useful for
   simple syntax substitutions.  For example, these entries
<programlisting>
mymap   /^(.*)@mydomain\.com$      \1
mymap   /^(.*)@otherdomain\.com$   guest
</programlisting>
   will remove the domain part for users with system usernames that end with
   <literal>@mydomain.com</>, and allow any user whose system name ends with
   <literal>@otherdomain.com</> to log in as <literal>guest</>.
  </para>

  <tip>
   <para>
    Keep in mind that by default, a regular expression can match just part of
    a string.  It's usually wise to use <literal>^</> and <literal>$</>, as
    shown in the above example, to force the match to be to the entire
    system username.
   </para>
  </tip>

  <para>
   The <filename>pg_ident.conf</filename> file is read on start-up and
   when the main server process receives a
   <systemitem>SIGHUP</systemitem><indexterm><primary>SIGHUP</primary></indexterm>
   signal. If you edit the file on an
   active system, you will need to signal the server
   (using <literal>pg_ctl reload</> or <literal>kill -HUP</>) to make it
   re-read the file.
  </para>

  <para>
   A <filename>pg_ident.conf</filename> file that could be used in
   conjunction with the <filename>pg_hba.conf</> file in <xref
   linkend="example-pg-hba.conf"> is shown in <xref
   linkend="example-pg-ident.conf">. In this example setup, anyone
   logged in to a machine on the 192.168 network that does not have the
   Unix user name <literal>bryanh</>, <literal>ann</>, or
   <literal>robert</> would not be granted access. Unix user
   <literal>robert</> would only be allowed access when he tries to
   connect as <productname>PostgreSQL</> user <literal>bob</>, not
   as <literal>robert</> or anyone else. <literal>ann</> would
   only be allowed to connect as <literal>ann</>. User
   <literal>bryanh</> would be allowed to connect as either
   <literal>bryanh</> himself or as <literal>guest1</>.
  </para>

  <example id="example-pg-ident.conf">
   <title>An example <filename>pg_ident.conf</> file</title>
<programlisting>
# 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
</programlisting>
  </example>
 </sect1>

 <sect1 id="auth-methods">
  <title>Authentication methods</title>
  <para>
   The following subsections describe the authentication methods in more detail.
  </para>

  <sect2 id="auth-trust">
   <title>Trust authentication</title>

   <para>
    When <literal>trust</> authentication is specified,
    <productname>PostgreSQL</productname> 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 <literal>database</> and
    <literal>user</> columns still apply.
    This method should only be used when there is adequate
    operating-system-level protection on connections to the server.
   </para>

   <para>
    <literal>trust</> authentication is appropriate and very
    convenient for local connections on a single-user workstation.  It
    is usually <emphasis>not</> appropriate by itself on a multiuser
    machine.  However, you might be able to use <literal>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
    <varname>unix_socket_permissions</varname> (and possibly
    <varname>unix_socket_group</varname>) configuration parameters as
    described in <xref linkend="runtime-config-connection">.  Or you
    could set the <varname>unix_socket_directory</varname>
    configuration parameter to place the socket file in a suitably
    restricted directory.
   </para>

   <para>
    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 <literal>host ... 127.0.0.1 ...</> line from
    <filename>pg_hba.conf</>, or change it to a
    non-<literal>trust</> authentication method.
   </para>

   <para>
    <literal>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 <filename>pg_hba.conf</> lines that specify
    <literal>trust</>.  It is seldom reasonable to use <literal>trust</>
    for any TCP/IP connections other than those from <systemitem>localhost</> (127.0.0.1).
   </para>

  </sect2>

  <sect2 id="auth-password">
   <title>Password authentication</title>

   <indexterm>
    <primary>MD5</>
   </indexterm>
   <indexterm>
    <primary>password</primary>
    <secondary>authentication</secondary>
   </indexterm>

   <para>
    The password-based authentication methods are <literal>md5</>
    and <literal>password</>. These methods operate
    similarly except for the way that the password is sent across the
    connection: respectively, MD5-hashed and clear-text.
   </para>

   <para>
    If you are at all concerned about password
    <quote>sniffing</> attacks then <literal>md5</> is preferred.
    Plain <literal>password</> should always be avoided if possible.
    However, <literal>md5</> cannot be used with the <xref
    linkend="guc-db-user-namespace"> feature.  If the connection is
    protected by SSL encryption then <literal>password</> can be used
    safely (though SSL certificate authentication might be a better
    choice if one is depending on using SSL).
   </para>

   <para>
    <productname>PostgreSQL</productname> database passwords are
    separate from operating system user passwords. The password for
    each database user is stored in the <literal>pg_authid</> system
    catalog. Passwords can be managed with the SQL commands
    <xref linkend="sql-createuser" endterm="sql-createuser-title"> and
    <xref linkend="sql-alteruser" endterm="sql-alteruser-title">,
    e.g., <userinput>CREATE USER foo WITH PASSWORD 'secret';</userinput>.
    By default, that is, if no password has been set up, the stored password
    is null and password authentication will always fail for that user.
   </para>

  </sect2>

  <sect2 id="gssapi-auth">
   <title>GSSAPI authentication</title>

   <indexterm zone="gssapi-auth">
    <primary>GSSAPI</primary>
   </indexterm>

   <para>
    <productname>GSSAPI</productname> is an industry-standard protocol
    for secure authentication defined in RFC 2743.
    <productname>PostgreSQL</productname> supports
    <productname>GSSAPI</productname> with <productname>Kerberos</productname>
    authentication according to RFC 1964. <productname>GSSAPI</productname>
    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 in clear unless
    <acronym>SSL</acronym> is used.
   </para>

   <para>
    When <productname>GSSAPI</productname> uses
    <productname>Kerberos</productname>, it uses a standard principal
    in the format
    <literal><replaceable>servicename</>/<replaceable>hostname</>@<replaceable>realm</></literal>. For information about the parts of the principal, and
    how to set up the required keys, see <xref linkend="kerberos-auth">.
    GSSAPI support has to be enabled when <productname>PostgreSQL</> is built;
    see <xref linkend="installation"> for more information.
   </para>

   <para>
    The following configuration options are supported for <productname>GSSAPI</productname>:
    <variablelist>
     <varlistentry>
      <term><literal>map</literal></term>
      <listitem>
       <para>
        Allows for mapping between system and database usernames. See
        <xref linkend="auth-username-maps"> for details.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>include_realm</literal></term>
      <listitem>
       <para>
        If set to <literal>1</>, the realm name from the authenticated user
        principal is included in the system user name that's passed through
        username mapping (<xref linkend="auth-username-maps">). This is
        useful for handling users from multiple realms.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>krb_realm</literal></term>
      <listitem>
       <para>
        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 username mapping
        is done.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2 id="sspi-auth">
   <title>SSPI authentication</title>

   <indexterm zone="sspi-auth">
    <primary>SSPI</primary>
   </indexterm>

   <para>
    <productname>SSPI</productname> is a <productname>Windows</productname>
    technology for secure authentication with single sign-on.
    <productname>PostgreSQL</productname> will use SSPI in
    <literal>negotiate</literal> mode, which will use
    <productname>Kerberos</productname> when possible and automatically
    fall back to <productname>NTLM</productname> in other cases.
    <productname>SSPI</productname> authentication only works when both
    server and client are running <productname>Windows</productname>.
   </para>

   <para>
    When using <productname>Kerberos</productname> authentication,
    <productname>SSPI</productname> works the same way
    <productname>GSSAPI</productname> does. See <xref linkend="gssapi-auth">
    for details.
   </para>

   <para>
    The following configuration options are supported for <productname>SSPI</productname>:
    <variablelist>
     <varlistentry>
      <term><literal>map</literal></term>
      <listitem>
       <para>
        Allows for mapping between system and database usernames. See
        <xref linkend="auth-username-maps"> for details.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>include_realm</literal></term>
      <listitem>
       <para>
        If set to <literal>1</>, the realm name from the authenticated user
        principal is included in the system user name that's passed through
        username mapping (<xref linkend="auth-username-maps">). This is
        useful for handling users from multiple realms.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>krb_realm</literal></term>
      <listitem>
       <para>
        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 username mapping
        is done.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2 id="kerberos-auth">
   <title>Kerberos authentication</title>

   <indexterm zone="kerberos-auth">
    <primary>Kerberos</primary>
   </indexterm>

   <note>
    <para>
     Native Kerberos authentication has been deprecated and should be used
     only for backward compatibility. New and upgraded installations are
     encouraged to use the industry-standard <productname>GSSAPI</productname>
     authentication (see <xref linkend="gssapi-auth">) instead.
    </para>
   </note>

   <para>
    <productname>Kerberos</productname> is an industry-standard secure
    authentication system suitable for distributed computing over a public
    network. A description of the <productname>Kerberos</productname> system
    is far beyond the scope of this document; in full generality it can be
    quite complex (yet powerful). The
    <ulink url="http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html">
    Kerberos <acronym>FAQ</></ulink> or
    <ulink url="http://web.mit.edu/kerberos/www/">MIT Kerberos page</ulink>
    can be good starting points for exploration.
    Several sources for <productname>Kerberos</> distributions exist.
    <productname>Kerberos</productname> provides secure authentication but
    does not encrypt queries or data passed over the network;  for that
    use <acronym>SSL</acronym>.
   </para>

   <para>
    <productname>PostgreSQL</> supports Kerberos version 5.  Kerberos
    support has to be enabled when <productname>PostgreSQL</> is built;
    see <xref linkend="installation"> for more information.
   </para>

   <para>
    <productname>PostgreSQL</> operates like a normal Kerberos service.
    The name of the service principal is
    <literal><replaceable>servicename</>/<replaceable>hostname</>@<replaceable>realm</></literal>.
   </para>

   <para>
    <replaceable>servicename</> can be set on the server side using the
    <xref linkend="guc-krb-srvname"> configuration parameter, and on the
    client side using the <literal>krbsrvname</> connection parameter. (See
    also <xref linkend="libpq-connect">.)  The installation default can be
    changed from the default <literal>postgres</literal> at build time using
    <literal>./configure --with-krb-srvnam=</><replaceable>whatever</>.
    In most environments,
    this parameter never needs to be changed. However, to support multiple
    <productname>PostgreSQL</> installations on the same host it is necessary.
    Some Kerberos implementations might also require a different service name,
    such as Microsoft Active Directory which requires the service name
    to be in uppercase (<literal>POSTGRES</literal>).
   </para>

   <para>
    <replaceable>hostname</> is the fully qualified host name of the
    server machine. The service principal's realm is the preferred realm
    of the server machine.
   </para>

   <para>
    Client principals must have their <productname>PostgreSQL</> database user
    name as their first component, for example
    <literal>pgusername@realm</>.  Alternatively, you can use a username
    mapping to map from the first component of the principal name to the
    database user name.  By default, the realm of the client is
    not checked by <productname>PostgreSQL</>. If you have cross-realm
    authentication enabled and need to verify the realm, use the
    <literal>krb_realm</> parameter, or enable <literal>include_realm</>
    and use username mapping to check the realm.
   </para>

   <para>
    Make sure that your server keytab file is readable (and preferably
    only readable) by the <productname>PostgreSQL</productname> server
    account.  (See also <xref linkend="postgres-user">.) The location
    of the key file is specified by the <xref
    linkend="guc-krb-server-keyfile"> configuration
    parameter. The default is
    <filename>/usr/local/pgsql/etc/krb5.keytab</> (or whichever
    directory was specified as <varname>sysconfdir</> at build time).
   </para>

   <para>
    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:
<screen>
<prompt>kadmin% </><userinput>ank -randkey postgres/server.my.domain.org</>
<prompt>kadmin% </><userinput>ktadd -k krb5.keytab postgres/server.my.domain.org</>
</screen>
   </para>

   <para>
    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 <literal>fred</>, both principal
    <literal>fred@EXAMPLE.COM</> and
    <literal>fred/users.example.com@EXAMPLE.COM</> could be used to
    authenticate to the database server.
   </para>

   <para>
    If you use <ulink url="http://modauthkerb.sf.net">
    <application>mod_auth_kerb</application></ulink>
    and <application>mod_perl</application> on your
    <productname>Apache</productname> web server, you can use
    <literal>AuthType KerberosV5SaveCredentials</literal> with a
    <application>mod_perl</application> script. This gives secure
    database access over the web, no extra passwords required.
   </para>

   <para>
    The following configuration options are supported for
    <productname>Kerberos</productname>:
    <variablelist>
     <varlistentry>
      <term><literal>map</literal></term>
      <listitem>
       <para>
        Allows for mapping between system and database usernames. See
        <xref linkend="auth-username-maps"> for details.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>include_realm</literal></term>
      <listitem>
       <para>
        If set to <literal>1</>, the realm name from the authenticated user
        principal is included in the system user name that's passed through
        username mapping (<xref linkend="auth-username-maps">). This is
        useful for handling users from multiple realms.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>krb_realm</literal></term>
      <listitem>
       <para>
        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 username mapping
        is done.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>krb_server_hostname</literal></term>
      <listitem>
       <para>
        Sets the host name part of the service principal.
        This, combined with <varname>krb_srvname</>, is used to generate
        the complete service principal, that is
        <varname>krb_srvname</><literal>/</><varname>krb_server_hostname</><literal>@</>REALM.
        If not set, the default is the server host name.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2 id="auth-ident">
   <title>Ident-based authentication</title>

   <indexterm>
    <primary>ident</primary>
   </indexterm>

   <para>
    The ident authentication method works by obtaining the client's
    operating system user name and using it as the allowed database user
    name (with an optional username mapping).
    The determination of the client's
    user name is the security-critical point, and it works differently
    depending on the connection type.
   </para>

   <para>
    The following configuration options are supported for <productname>ident</productname>:
    <variablelist>
     <varlistentry>
      <term><literal>map</literal></term>
      <listitem>
       <para>
        Allows for mapping between system and database usernames. See
        <xref linkend="auth-username-maps"> for details.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <sect3>
    <title>Ident Authentication over TCP/IP</title>

   <para>
    The <quote>Identification Protocol</quote> 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 <quote>What user initiated the
    connection that goes out of your port <replaceable>X</replaceable>
    and connects to my port <replaceable>Y</replaceable>?</quote>.
    Since <productname>PostgreSQL</> knows both <replaceable>X</> and
    <replaceable>Y</> when a physical connection is established, it
    can interrogate the ident server on the host of the connecting
    client and could theoretically determine the operating system user
    for any given connection this way.
   </para>

   <para>
    The drawback of this procedure is that it depends on the integrity
    of the client: if the client machine is untrusted or compromised
    an attacker could run just about any program on port 113 and
    return any user name he chooses. This authentication method is
    therefore only appropriate for closed networks where each client
    machine is under tight control and where the database and system
    administrators operate in close contact. In other words, you must
    trust the machine running the ident server.
    Heed the warning:
    <blockquote>
     <attribution>RFC 1413</attribution>
     <para>
      The Identification Protocol is not intended as an authorization
      or access control protocol.
     </para>
    </blockquote>
   </para>

   <para>
    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 <emphasis>must not</> be
    used when using the ident server with <productname>PostgreSQL</>,
    since <productname>PostgreSQL</> does not have any way to decrypt the
    returned string to determine the actual user name.
   </para>
   </sect3>

   <sect3>
    <title>Ident Authentication over Local Sockets</title>

   <para>
    On systems supporting <symbol>SO_PEERCRED</symbol> requests for
    Unix-domain sockets (currently <systemitem
    class="osname">Linux</>, <systemitem class="osname">FreeBSD</>,
    <systemitem class="osname">NetBSD</>, <systemitem class="osname">OpenBSD</>,
    <systemitem class="osname">BSD/OS</>, and <systemitem class="osname">Solaris</systemitem>), ident authentication can also
    be applied to local connections. In this case, no security risk is added by
    using ident authentication; indeed it is a preferable choice for
    local connections on such systems.
   </para>

    <para>
     On systems without <symbol>SO_PEERCRED</> requests, ident
     authentication is only available for TCP/IP connections. As a
     work-around, it is possible to specify the <systemitem
     class="systemname">localhost</> address <systemitem
     class="systemname">127.0.0.1</> and make connections to this
     address.  This method is trustworthy to the extent that you trust
     the local ident server.
    </para>
    </sect3>

  </sect2>

  <sect2 id="auth-ldap">
   <title>LDAP authentication</title>

   <indexterm zone="auth-ldap">
    <primary>LDAP</primary>
   </indexterm>

   <para>
    This authentication method operates similarly to
    <literal>password</literal> 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.
   </para>

   <para>
    The server will bind to the distinguished name constructed as
    <replaceable>prefix</> <replaceable>username</> <replaceable>suffix</>.
    Typically, the <replaceable>prefix</> parameter is used to specify
    <literal>cn=</>, or <replaceable>DOMAIN</><literal>\</> in an Active
    Directory environment.  <replaceable>suffix</> is used to specify the
    remaining part of the DN in a non-Active Directory environment.
   </para>

   <para>
    The following configuration options are supported for LDAP:
    <variablelist>
     <varlistentry>
      <term><literal>ldapserver</literal></term>
      <listitem>
       <para>
        Name or IP of LDAP server to connect to.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>ldapprefix</literal></term>
      <listitem>
       <para>
        String to prepend to the username when forming the DN to bind as.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>ldapsuffix</literal></term>
      <listitem>
       <para>
        String to append to the username when forming the DN to bind as.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>ldapport</literal></term>
      <listitem>
       <para>
        Port number on LDAP server to connect to. If no port is specified,
        the default port in the LDAP library will be used.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><literal>ldaptls</literal></term>
      <listitem>
       <para>
        Set to <literal>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 &mdash; the connection to the client
        will still be unencrypted unless SSL is used.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <note>
    <para>
     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, for example:
    </para>
   </note>
    <synopsis>
ldapserver=ldap.example.net ldapprefix="cn=" ldapsuffix=", dc=example, dc=net"
    </synopsis>

  </sect2>

  <sect2 id="auth-cert">
   <title>Certificate authentication</title>

   <indexterm zone="auth-cert">
    <primary>Certificate</primary>
   </indexterm>

   <para>
    This authentication method uses SSL client certificates to perform
    authentication. It is therefore only available for SSL connections.
    When using this authentication method, the server will require that
    the client provide a valid certificate. No password prompt will be sent
    to the client. The <literal>cn</literal> attribute of the certificate
    will be compared to the requested database username, and if they match
    the login will be allowed.  Username mapping can be used to allow
    <literal>cn</literal> to be different from the database username.
   </para>

   <para>
    The following configuration options are supported for SSL certificate
    authentication:
    <variablelist>
     <varlistentry>
      <term><literal>map</literal></term>
      <listitem>
       <para>
        Allows for mapping between system and database usernames. See
        <xref linkend="auth-username-maps"> for details.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </sect2>

  <sect2 id="auth-pam">
   <title>PAM authentication</title>

   <indexterm zone="auth-pam">
    <primary>PAM</primary>
   </indexterm>

   <para>
    This authentication method operates similarly to
    <literal>password</literal> except that it uses PAM (Pluggable
    Authentication Modules) as the authentication mechanism. The
    default PAM service name is <literal>postgresql</literal>.
    PAM is used only to validate user name/password pairs.
    Therefore the user must already exist in the database before PAM
    can be used for authentication.  For more information about
    PAM, please read the <ulink url="http://www.kernel.org/pub/linux/libs/pam/">
    <productname>Linux-PAM</> Page</ulink>
    and the <ulink url="http://www.sun.com/software/solaris/pam/">
    <systemitem class="osname">Solaris</> PAM Page</ulink>.
   </para>

   <para>
    The following configuration options are supported for PAM:
    <variablelist>
     <varlistentry>
      <term><literal>pamservice</literal></term>
      <listitem>
       <para>
        PAM service name.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <note>
    <para>
     If PAM is set up to read <filename>/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.
    </para>
   </note>
  </sect2>
 </sect1>

  <sect1 id="client-authentication-problems">
   <title>Authentication problems</title>

   <para>
    Authentication failures and related problems generally
    manifest themselves through error messages like the following:
   </para>

   <para>
<programlisting>
FATAL:  no pg_hba.conf entry for host "123.123.123.123", user "andym", database "testdb"
</programlisting>
    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 <filename>pg_hba.conf</filename>
    configuration file.
   </para>

   <para>
<programlisting>
FATAL:  Password authentication failed for user "andym"
</programlisting>
    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 <filename>pg_hba.conf</filename> file. Check
    the password you are providing, or check your Kerberos or ident
    software if the complaint mentions one of those authentication
    types.
   </para>

   <para>
<programlisting>
FATAL:  user "andym" does not exist
</programlisting>
    The indicated database user name was not found.
   </para>

   <para>
<programlisting>
FATAL:  database "testdb" does not exist
</programlisting>
    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.
   </para>

   <tip>
   <para>
    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 log.
   </para>
   </tip>
  </sect1>

 </chapter>
