Allow SSL configuration to be updated at SIGHUP.

It is no longer necessary to restart the server to enable, disable,
or reconfigure SSL.  Instead, we just create a new SSL_CTX struct
(by re-reading all relevant files) whenever we get SIGHUP.  Testing
shows that this is fast enough that it shouldn't be a problem.

In conjunction with that, downgrade the logic that complains about
pg_hba.conf "hostssl" lines when SSL isn't active: now that's just
a warning condition not an error.

An issue that still needs to be addressed is what shall we do with
passphrase-protected server keys?  As this stands, the server would
demand the passphrase again on every SIGHUP, which is certainly
impractical.  But the case was only barely supported before, so that
does not seem a sufficient reason to hold up committing this patch.

Andreas Karlsson, reviewed by Michael Banck and Michael Paquier

Discussion: https://postgr.es/m/556A6E8A.9030400@proxel.se

doc/src/sgml/client-auth.sgml

@@ -156,9 +156,11 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
       <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
+       <acronym>SSL</acronym> must be enabled
        by setting the <xref linkend="guc-ssl"> configuration parameter (see
        <xref linkend="ssl-tcp"> for more information).
+       Otherwise, the <literal>hostssl</literal> record is ignored except for
+       logging a warning that it cannot match any connections.
       </para>
      </listitem>
     </varlistentry>

doc/src/sgml/config.sgml

@@ -958,10 +958,10 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Enables <acronym>SSL</> connections. Please read
-        <xref linkend="ssl-tcp"> before using this. The default
-        is <literal>off</>. This parameter can only be set at server
-        start.  <acronym>SSL</> communication is only possible with
-        TCP/IP connections.
+        <xref linkend="ssl-tcp"> before using this.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is <literal>off</>.
        </para>
       </listitem>
      </varlistentry>
@@ -975,11 +975,16 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Specifies the name of the file containing the SSL server certificate
-        authority (CA).  The default is empty, meaning no CA file is loaded,
-        and client certificate verification is not performed.  (In previous
-        releases of PostgreSQL, the name of this file was hard-coded
-        as <filename>root.crt</filename>.)  Relative paths are relative to the
-        data directory.  This parameter can only be set at server start.
+        authority (CA).
+        Relative paths are relative to the data directory.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is empty, meaning no CA file is loaded,
+        and client certificate verification is not performed.
+       </para>
+       <para>
+        In previous releases of PostgreSQL, the name of this file was
+        hard-coded as <filename>root.crt</filename>.
        </para>
       </listitem>
      </varlistentry>
@@ -993,9 +998,10 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Specifies the name of the file containing the SSL server certificate.
-        The default is <filename>server.crt</filename>.  Relative paths are
-        relative to the data directory.  This parameter can only be set at
-        server start.
+        Relative paths are relative to the data directory.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is <filename>server.crt</filename>.
        </para>
       </listitem>
      </varlistentry>
@@ -1009,11 +1015,15 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Specifies the name of the file containing the SSL server certificate
-        revocation list (CRL).  The default is empty, meaning no CRL file is
-        loaded.  (In previous releases of PostgreSQL, the name of this file was
-        hard-coded as <filename>root.crl</filename>.)  Relative paths are
-        relative to the data directory.  This parameter can only be set at
-        server start.
+        revocation list (CRL).
+        Relative paths are relative to the data directory.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is empty, meaning no CRL file is loaded.
+       </para>
+       <para>
+        In previous releases of PostgreSQL, the name of this file was
+        hard-coded as <filename>root.crl</filename>.
        </para>
       </listitem>
      </varlistentry>
@@ -1027,9 +1037,10 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Specifies the name of the file containing the SSL server private key.
-        The default is <filename>server.key</filename>.  Relative paths are
-        relative to the data directory.  This parameter can only be set at
-        server start.
+        Relative paths are relative to the data directory.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is <filename>server.key</filename>.
        </para>
       </listitem>
      </varlistentry>
@@ -1046,10 +1057,12 @@ include_dir 'conf.d'
         used on secure connections.  See
         the <citerefentry><refentrytitle>ciphers</></citerefentry> manual page
         in the <application>OpenSSL</> package for the syntax of this setting
-        and a list of supported values.  The default value is
-        <literal>HIGH:MEDIUM:+3DES:!aNULL</>.  It is usually reasonable,
-        unless you have specific security requirements.  This parameter can only
-        be set at server start.
+        and a list of supported values.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default value is <literal>HIGH:MEDIUM:+3DES:!aNULL</>.  The
+        default is usually a reasonable choice unless you have specific
+        security requirements.
        </para>
 
        <para>
@@ -1113,7 +1126,7 @@ include_dir 'conf.d'
      </varlistentry>
 
      <varlistentry id="guc-ssl-prefer-server-ciphers" xreflabel="ssl_prefer_server_ciphers">
-      <term><varname>ssl_prefer_server_ciphers</varname> (<type>bool</type>)
+      <term><varname>ssl_prefer_server_ciphers</varname> (<type>boolean</type>)
       <indexterm>
        <primary><varname>ssl_prefer_server_ciphers</> configuration parameter</primary>
       </indexterm>
@@ -1121,8 +1134,10 @@ include_dir 'conf.d'
       <listitem>
        <para>
         Specifies whether to use the server's SSL cipher preferences, rather
-        than the client's.  The default is true.  This parameter can only be
-        set at server start.
+        than the client's.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is <literal>true</>.
        </para>
 
        <para>
@@ -1145,19 +1160,18 @@ include_dir 'conf.d'
        <para>
         Specifies the name of the curve to use in <acronym>ECDH</> key
         exchange.  It needs to be supported by all clients that connect.
-        It does not need to be same curve as used by server's Elliptic
-        Curve key.  The default is <literal>prime256v1</>.  This parameter
-        can only be set at server start.
+        It does not need to be the same curve used by the server's Elliptic
+        Curve key.
+        This parameter can only be set in the <filename>postgresql.conf</>
+        file or on the server command line.
+        The default is <literal>prime256v1</>.
        </para>
 
        <para>
-        OpenSSL names for most common curves:
+        OpenSSL names for the most common curves are:
         <literal>prime256v1</> (NIST P-256),
         <literal>secp384r1</> (NIST P-384),
         <literal>secp521r1</> (NIST P-521).
-       </para>
-
-       <para>
         The full list of available curves can be shown with the command
         <command>openssl ecparam -list_curves</command>.  Not all of them
         are usable in <acronym>TLS</> though.
@@ -3003,7 +3017,7 @@ include_dir 'conf.d'
      </varlistentry>
 
      <varlistentry id="guc-track-commit-timestamp" xreflabel="track_commit_timestamp">
-      <term><varname>track_commit_timestamp</varname> (<type>bool</type>)
+      <term><varname>track_commit_timestamp</varname> (<type>boolean</type>)
       <indexterm>
        <primary><varname>track_commit_timestamp</> configuration parameter</primary>
       </indexterm>

doc/src/sgml/runtime.sgml

@@ -2285,11 +2285,20 @@ pg_dumpall -p 5432 | psql -d postgres -p 5433
   </table>
 
    <para>
-    The files <filename>server.key</>, <filename>server.crt</>,
-    <filename>root.crt</filename>, and <filename>root.crl</filename>
-    (or their configured alternative names)
-    are only examined during server start; so you must restart
-    the server for changes in them to take effect.
+    The server reads these files at server start and whenever the server
+    configuration is reloaded.  On <systemitem class="osname">Windows</>
+    systems, they are also re-read whenever a new backend process is spawned
+    for a new client connection.
+   </para>
+
+   <para>
+    If an error in these files is detected at server start, the server will
+    refuse to start.  But if an error is detected during a configuration
+    reload, the files are ignored and the old values continue to be used.
+    On <systemitem class="osname">Windows</> systems, if an error in these
+    files is detected at backend start, that backend will be unable to
+    establish an SSL connection.  In all these cases, the error condition is
+    reported in the server log.
    </para>
   </sect2>