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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AUTH-METHODS"
>20.2. Authentication methods</A
></H1
><P
> The following subsections describe the authentication methods in more detail.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AUTH-TRUST"
>20.2.1. Trust authentication</A
></H2
><P
> When <TT
CLASS="LITERAL"
>trust</TT
> authentication is specified,
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> assumes that anyone who can
connect to the server is authorized to access the database with
whatever database user name they specify (including superusers).
Of course, restrictions made in the <TT
CLASS="LITERAL"
>database</TT
> and
<TT
CLASS="LITERAL"
>user</TT
> columns still apply.
This method should only be used when there is adequate
operating-system-level protection on connections to the server.
</P
><P
> <TT
CLASS="LITERAL"
>trust</TT
> authentication is appropriate and very
convenient for local connections on a single-user workstation. It
is usually <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> appropriate by itself on a multiuser
machine. However, you may be able to use <TT
CLASS="LITERAL"
>trust</TT
> 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
<TT
CLASS="VARNAME"
>unix_socket_permissions</TT
> (and possibly
<TT
CLASS="VARNAME"
>unix_socket_group</TT
>) configuration parameters as
described in <A
HREF="runtime-config-connection.html"
>Section 17.3</A
>. Or you
could set the <TT
CLASS="VARNAME"
>unix_socket_directory</TT
>
configuration parameter to place the socket file in a suitably
restricted directory.
</P
><P
> Setting file-system permissions only helps for Unix-socket connections.
Local TCP/IP connections are not restricted by it; therefore, if you want
to use file-system permissions for local security, remove the <TT
CLASS="LITERAL"
>host ...
127.0.0.1 ...</TT
> line from <TT
CLASS="FILENAME"
>pg_hba.conf</TT
>, or change it to a
non-<TT
CLASS="LITERAL"
>trust</TT
> authentication method.
</P
><P
> <TT
CLASS="LITERAL"
>trust</TT
> 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 <TT
CLASS="FILENAME"
>pg_hba.conf</TT
> lines that specify
<TT
CLASS="LITERAL"
>trust</TT
>. It is seldom reasonable to use <TT
CLASS="LITERAL"
>trust</TT
>
for any TCP/IP connections other than those from <SPAN
CLASS="SYSTEMITEM"
>localhost</SPAN
> (127.0.0.1).
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AUTH-PASSWORD"
>20.2.2. Password authentication</A
></H2
><A
NAME="AEN21841"
></A
><A
NAME="AEN21843"
></A
><A
NAME="AEN21845"
></A
><P
> The password-based authentication methods are <TT
CLASS="LITERAL"
>md5</TT
>,
<TT
CLASS="LITERAL"
>crypt</TT
>, and <TT
CLASS="LITERAL"
>password</TT
>. These methods operate
similarly except for the way that the password is sent across the
connection: respectively, MD5-hashed, crypt-encrypted, and clear-text.
A limitation is that the <TT
CLASS="LITERAL"
>crypt</TT
> method does not work with
passwords that have been encrypted in <TT
CLASS="STRUCTNAME"
>pg_authid</TT
>.
</P
><P
> If you are at all concerned about password
<SPAN
CLASS="QUOTE"
>"sniffing"</SPAN
> attacks then <TT
CLASS="LITERAL"
>md5</TT
> is preferred, with
<TT
CLASS="LITERAL"
>crypt</TT
> to be used only if you must support pre-7.2
clients. Plain <TT
CLASS="LITERAL"
>password</TT
> should be avoided especially for
connections over the open Internet (unless you use <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
>,
<ACRONYM
CLASS="ACRONYM"
>SSH</ACRONYM
>, or another
communications security wrapper around the connection).
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> database passwords are
separate from operating system user passwords. The password for
each database user is stored in the <TT
CLASS="LITERAL"
>pg_authid</TT
> system
catalog. Passwords can be managed with the SQL commands
<A
HREF="sql-createuser.html"
><I
>CREATE USER</I
></A
> and
<A
HREF="sql-alteruser.html"
><I
>ALTER USER</I
></A
>,
e.g., <KBD
CLASS="USERINPUT"
>CREATE USER foo WITH PASSWORD 'secret';</KBD
>.
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.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="KERBEROS-AUTH"
>20.2.3. Kerberos authentication</A
></H2
><A
NAME="AEN21869"
></A
><P
> <SPAN
CLASS="PRODUCTNAME"
>Kerberos</SPAN
> is an industry-standard secure
authentication system suitable for distributed computing over a public
network. A description of the <SPAN
CLASS="PRODUCTNAME"
>Kerberos</SPAN
> system
is far beyond the scope of this document; in full generality it can be
quite complex (yet powerful). The
<A
HREF="http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html"
TARGET="_top"
> Kerberos <ACRONYM
CLASS="ACRONYM"
>FAQ</ACRONYM
></A
> or
<A
HREF="http://web.mit.edu/kerberos/www/"
TARGET="_top"
>MIT Kerberos page</A
>
can be good starting points for exploration.
Several sources for <SPAN
CLASS="PRODUCTNAME"
>Kerberos</SPAN
> distributions exist.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> supports Kerberos version 5. Kerberos
support has to be enabled when <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is built;
see <A
HREF="installation.html"
>Chapter 14</A
> for more information.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> operates like a normal Kerberos service.
The name of the service principal is
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>servicename</I
></TT
>/<TT
CLASS="REPLACEABLE"
><I
>hostname</I
></TT
>@<TT
CLASS="REPLACEABLE"
><I
>realm</I
></TT
></TT
>.
</P
><P
> <TT
CLASS="REPLACEABLE"
><I
>servicename</I
></TT
> can be set on the server side using the
<A
HREF="runtime-config-connection.html#GUC-KRB-SRVNAME"
>krb_srvname</A
> configuration parameter, and on the
client side using the <TT
CLASS="LITERAL"
>krbsrvname</TT
> connection parameter. (See
also <A
HREF="libpq.html#LIBPQ-CONNECT"
>Section 28.1</A
>.) The installation default can be
changed from the default <TT
CLASS="LITERAL"
>postgres</TT
> at build time using
<TT
CLASS="LITERAL"
>./configure --with-krb-srvnam=whatever</TT
>. In most environments,
this parameter never needs to be changed. However, to support multiple
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installations on the same host it is necessary.
Some Kerberos implementations may also require a different service name,
such as Microsoft Active Directory which requires the service name
to be in uppercase (<TT
CLASS="LITERAL"
>POSTGRES</TT
>).
</P
><P
> <TT
CLASS="REPLACEABLE"
><I
>hostname</I
></TT
> is the fully qualified host name of the
server machine. The service principal's realm is the preferred realm
of the server machine.
</P
><P
> Client principals must have their <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> database user
name as their first component, for example
<TT
CLASS="LITERAL"
>pgusername/otherstuff@realm</TT
>. At present the realm of
the client is not checked by <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>; so if you
have cross-realm authentication enabled, then any principal in any
realm that can communicate with yours will be accepted.
</P
><P
> Make sure that your server keytab file is readable (and preferably
only readable) by the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server
account. (See also <A
HREF="runtime.html#POSTGRES-USER"
>Section 16.1</A
>.) The location
of the key file is specified by the <A
HREF="runtime-config-connection.html#GUC-KRB-SERVER-KEYFILE"
>krb_server_keyfile</A
> configuration
parameter. The default is
<TT
CLASS="FILENAME"
>/usr/local/pgsql/etc/krb5.keytab</TT
> (or whichever
directory was specified as <TT
CLASS="VARNAME"
>sysconfdir</TT
> at build time).
</P
><P
> 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:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>kadmin% </SAMP
><KBD
CLASS="USERINPUT"
>ank -randkey postgres/server.my.domain.org</KBD
>
<SAMP
CLASS="PROMPT"
>kadmin% </SAMP
><KBD
CLASS="USERINPUT"
>ktadd -k krb5.keytab postgres/server.my.domain.org</KBD
></PRE
><P>
</P
><P
> 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 <TT
CLASS="LITERAL"
>fred</TT
>, both principal
<TT
CLASS="LITERAL"
>fred@EXAMPLE.COM</TT
> and
<TT
CLASS="LITERAL"
>fred/users.example.com@EXAMPLE.COM</TT
> could be used to
authenticate to the database server.
</P
><P
> If you use <A
HREF="http://modauthkerb.sf.net"
TARGET="_top"
> <SPAN
CLASS="APPLICATION"
>mod_auth_kerb</SPAN
></A
>
and <SPAN
CLASS="APPLICATION"
>mod_perl</SPAN
> on your
<SPAN
CLASS="PRODUCTNAME"
>Apache</SPAN
> web server, you can use
<TT
CLASS="LITERAL"
>AuthType KerberosV5SaveCredentials</TT
> with a
<SPAN
CLASS="APPLICATION"
>mod_perl</SPAN
> script. This gives secure
database access over the web, no extra passwords required.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AUTH-IDENT"
>20.2.4. Ident-based authentication</A
></H2
><A
NAME="AEN21928"
></A
><P
> The ident authentication method works by obtaining the client's
operating system user name, then determining the allowed database
user names using a map file that lists the permitted
corresponding pairs of names. The determination of the client's
user name is the security-critical point, and it works differently
depending on the connection type.
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN21931"
>20.2.4.1. Ident Authentication over TCP/IP</A
></H3
><P
> The <SPAN
CLASS="QUOTE"
>"Identification Protocol"</SPAN
> is described in
<I
CLASS="CITETITLE"
>RFC 1413</I
>. 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 <SPAN
CLASS="QUOTE"
>"What user initiated the
connection that goes out of your port <TT
CLASS="REPLACEABLE"
><I
>X</I
></TT
>
and connects to my port <TT
CLASS="REPLACEABLE"
><I
>Y</I
></TT
>?"</SPAN
>.
Since <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> knows both <TT
CLASS="REPLACEABLE"
><I
>X</I
></TT
> and
<TT
CLASS="REPLACEABLE"
><I
>Y</I
></TT
> 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.
</P
><P
> 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:
<A
NAME="AEN21943"
></A
><TABLE
BORDER="0"
WIDTH="100%"
CELLSPACING="0"
CELLPADDING="0"
CLASS="BLOCKQUOTE"
><TR
><TD
WIDTH="10%"
VALIGN="TOP"
> </TD
><TD
VALIGN="TOP"
><P
> The Identification Protocol is not intended as an authorization
or access control protocol.
</P
></TD
><TD
WIDTH="10%"
VALIGN="TOP"
> </TD
></TR
><TR
><TD
COLSPAN="2"
ALIGN="RIGHT"
VALIGN="TOP"
>--<SPAN
CLASS="ATTRIBUTION"
>RFC 1413</SPAN
></TD
><TD
WIDTH="10%"
> </TD
></TR
></TABLE
>
</P
><P
> 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 <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>must not</I
></SPAN
> be
used when using the ident server with <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>,
since <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does not have any way to decrypt the
returned string to determine the actual user name.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN21950"
>20.2.4.2. Ident Authentication over Local Sockets</A
></H3
><P
> On systems supporting <TT
CLASS="SYMBOL"
>SO_PEERCRED</TT
> requests for
Unix-domain sockets (currently <SPAN
CLASS="SYSTEMITEM"
>Linux</SPAN
>, <SPAN
CLASS="SYSTEMITEM"
>FreeBSD</SPAN
>,
<SPAN
CLASS="SYSTEMITEM"
>NetBSD</SPAN
>, <SPAN
CLASS="SYSTEMITEM"
>OpenBSD</SPAN
>,
and <SPAN
CLASS="SYSTEMITEM"
>BSD/OS</SPAN
>), 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.
</P
><P
> On systems without <TT
CLASS="SYMBOL"
>SO_PEERCRED</TT
> requests, ident
authentication is only available for TCP/IP connections. As a
work-around, it is possible to specify the <SPAN
CLASS="SYSTEMITEM"
>localhost</SPAN
> address <SPAN
CLASS="SYSTEMITEM"
>127.0.0.1</SPAN
> and make connections to this
address. This method is trustworthy to the extent that you trust
the local ident server.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AUTH-IDENT-MAPS"
>20.2.4.3. Ident Maps</A
></H3
><P
> When using ident-based authentication, after having determined the
name of the operating system user that initiated the connection,
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> checks whether that user is
allowed to connect as the database user he is requesting to connect
as. This is controlled by the ident map argument that follows the
<TT
CLASS="LITERAL"
>ident</TT
> key word in the <TT
CLASS="FILENAME"
>pg_hba.conf</TT
>
file. There is a predefined ident map <TT
CLASS="LITERAL"
>sameuser</TT
>,
which allows any operating system user to connect as the database
user of the same name (if the latter exists). Other maps must be
created manually.
</P
><P
> Ident maps other than <TT
CLASS="LITERAL"
>sameuser</TT
> are defined in the
ident map file, which by default is named
<TT
CLASS="FILENAME"
>pg_ident.conf</TT
><A
NAME="AEN21973"
></A
>
and is stored in the
cluster's data directory. (It is possible to place the map file
elsewhere, however; see the <A
HREF="runtime-config-file-locations.html#GUC-IDENT-FILE"
>ident_file</A
>
configuration parameter.)
The ident map file contains lines of the general form:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>map-name</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>ident-username</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>database-username</I
></TT
></PRE
><P>
Comments and whitespace are handled in the same way as in
<TT
CLASS="FILENAME"
>pg_hba.conf</TT
>. The
<TT
CLASS="REPLACEABLE"
><I
>map-name</I
></TT
> is an arbitrary name that will be used to
refer to this mapping in <TT
CLASS="FILENAME"
>pg_hba.conf</TT
>. The other
two fields specify which operating system user is allowed to connect
as which database user. The same <TT
CLASS="REPLACEABLE"
><I
>map-name</I
></TT
> can be
used repeatedly to specify more user-mappings within a single map.
There is no restriction regarding how many database users a given
operating system user may correspond to, nor vice versa.
</P
><P
> The <TT
CLASS="FILENAME"
>pg_ident.conf</TT
> file is read on start-up and
when the main server process (<TT
CLASS="COMMAND"
>postmaster</TT
>) receives a
<SPAN
CLASS="SYSTEMITEM"
>SIGHUP</SPAN
><A
NAME="AEN21988"
></A
>
signal. If you edit the file on an
active system, you will need to signal the <TT
CLASS="COMMAND"
>postmaster</TT
>
(using <TT
CLASS="LITERAL"
>pg_ctl reload</TT
> or <TT
CLASS="LITERAL"
>kill -HUP</TT
>) to make it
re-read the file.
</P
><P
> A <TT
CLASS="FILENAME"
>pg_ident.conf</TT
> file that could be used in
conjunction with the <TT
CLASS="FILENAME"
>pg_hba.conf</TT
> file in <A
HREF="client-authentication.html#EXAMPLE-PG-HBA.CONF"
>Example 20-1</A
> is shown in <A
HREF="auth-methods.html#EXAMPLE-PG-IDENT.CONF"
>Example 20-2</A
>. In this example setup, anyone
logged in to a machine on the 192.168 network that does not have the
Unix user name <TT
CLASS="LITERAL"
>bryanh</TT
>, <TT
CLASS="LITERAL"
>ann</TT
>, or
<TT
CLASS="LITERAL"
>robert</TT
> would not be granted access. Unix user
<TT
CLASS="LITERAL"
>robert</TT
> would only be allowed access when he tries to
connect as <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user <TT
CLASS="LITERAL"
>bob</TT
>, not
as <TT
CLASS="LITERAL"
>robert</TT
> or anyone else. <TT
CLASS="LITERAL"
>ann</TT
> would
only be allowed to connect as <TT
CLASS="LITERAL"
>ann</TT
>. User
<TT
CLASS="LITERAL"
>bryanh</TT
> would be allowed to connect as either
<TT
CLASS="LITERAL"
>bryanh</TT
> himself or as <TT
CLASS="LITERAL"
>guest1</TT
>.
</P
><DIV
CLASS="EXAMPLE"
><A
NAME="EXAMPLE-PG-IDENT.CONF"
></A
><P
><B
>Example 20-2. An example <TT
CLASS="FILENAME"
>pg_ident.conf</TT
> file</B
></P
><PRE
CLASS="PROGRAMLISTING"
># MAPNAME IDENT-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</PRE
></DIV
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AUTH-PAM"
>20.2.5. PAM authentication</A
></H2
><A
NAME="AEN22016"
></A
><P
> This authentication method operates similarly to
<TT
CLASS="LITERAL"
>password</TT
> except that it uses PAM (Pluggable
Authentication Modules) as the authentication mechanism. The
default PAM service name is <TT
CLASS="LITERAL"
>postgresql</TT
>. You can
optionally supply your own service name after the <TT
CLASS="LITERAL"
>pam</TT
>
key word in the file <TT
CLASS="FILENAME"
>pg_hba.conf</TT
>.
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 <A
HREF="http://www.kernel.org/pub/linux/libs/pam/"
TARGET="_top"
> <SPAN
CLASS="PRODUCTNAME"
>Linux-PAM</SPAN
> Page</A
>
and the <A
HREF="http://www.sun.com/software/solaris/pam/"
TARGET="_top"
> <SPAN
CLASS="SYSTEMITEM"
>Solaris</SPAN
> PAM Page</A
>.
</P
></DIV
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