Add BSD authentication method.

Create a "bsd" auth method that works the same as "password" so far as
clients are concerned, but calls the BSD Authentication service to
check the password.  This is currently only available on OpenBSD.

Marisa Emerson, reviewed by Thomas Munro

doc/src/sgml/client-auth.sgml

@@ -522,6 +522,16 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal>bsd</></term>
+        <listitem>
+         <para>
+          Authenticate using the BSD Authentication service provided by the
+          operating system. See <xref linkend="auth-bsd"> for details.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
 
       </para>
@@ -1662,6 +1672,41 @@ host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
     </para>
    </note>
   </sect2>
+
+  <sect2 id="auth-bsd">
+   <title>BSD Authentication</title>
+
+   <indexterm zone="auth-bsd">
+    <primary>BSD Authentication</primary>
+   </indexterm>
+
+   <para>
+    This authentication method operates similarly to
+    <literal>password</literal> 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.
+   </para>
+
+   <para>
+    BSD Authentication in <productname>PostgreSQL</> uses
+    the <literal>auth-postgresql</literal> login type and authenticates with
+    the <literal>postgresql</literal> login class if that's defined
+    in <filename>login.conf</filename>. By default that login class does not
+    exist, and <productname>PostgreSQL</> will use the default login class.
+   </para>
+
+   <note>
+    <para>
+     To use BSD Authentication, the PostgreSQL user account (that is, the
+     operating system user running the server) must first be added to
+     the <literal>auth</literal> group.  The <literal>auth</literal> group
+     exists by default on OpenBSD systems.
+    </para>
+   </note>
+  </sect2>
  </sect1>
 
   <sect1 id="client-authentication-problems">

doc/src/sgml/installation.sgml

@@ -792,6 +792,17 @@ su - postgres
        </listitem>
       </varlistentry>
 
+      <varlistentry>
+       <term><option>--with-bsd-auth</option></term>
+       <listitem>
+        <para>
+         Build with BSD Authentication support.
+         (The BSD Authentication framework is
+         currently only available on OpenBSD.)
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry>
        <term><option>--with-ldap</option></term>
        <listitem>