</varlistentry>
 
      <varlistentry id="guc-log-connections" xreflabel="log_connections">
-      <term><varname>log_connections</varname> (<type>boolean</type>)
+      <term><varname>log_connections</varname> (<type>string</type>)
       <indexterm>
        <primary><varname>log_connections</varname> configuration parameter</primary>
       </indexterm>
       </term>
       <listitem>
        <para>
-        Causes each attempted connection to the server to be logged,
-        as well as successful completion of both client authentication (if
-        necessary) and authorization.
+        Causes aspects of each connection to the server to be logged.
+        The default is the empty string, <literal>''</literal>, which
+        disables all connection logging. The following options may be
+        specified alone or in a comma-separated list:
+       </para>
+
+       <table id="log-connections-options">
+        <title>Log Connection Options</title>
+        <tgroup cols="2">
+         <colspec colname="col1" colwidth="1*"/>
+         <colspec colname="col2" colwidth="2*"/>
+         <thead>
+          <row>
+           <entry>Name</entry>
+           <entry>Description</entry>
+          </row>
+         </thead>
+         <tbody>
+          <row>
+           <entry><literal>receipt</literal></entry>
+           <entry>Logs receipt of a connection.</entry>
+          </row>
+
+          <row>
+           <entry><literal>authentication</literal></entry>
+           <entry>
+            Logs the original identity used by an authentication method
+            to identify a user. In most cases, the identity string
+            matches the <productname>PostgreSQL</productname> username,
+            but some third-party authentication methods may alter the
+            original user identifier before the server stores it. Failed
+            authentication is always logged regardless of the value of
+            this setting.
+           </entry>
+          </row>
+
+          <row>
+           <entry><literal>authorization</literal></entry>
+           <entry>
+            Logs successful completion of authorization. At this point
+            the connection has been established but the backend is not
+            yet fully set up. The log message includes the authorized
+            username as well as the database name and application name,
+            if applicable.
+           </entry>
+          </row>
+
+          <row>
+           <entry><literal>all</literal></entry>
+           <entry>
+            A convenience alias equivalent to specifying all options. If
+            <literal>all</literal> is specified in a list of other
+            options, all connection aspects will be logged.
+           </entry>
+          </row>
+
+         </tbody>
+        </tgroup>
+       </table>
+
+       <para>
+        Disconnection logging is separately controlled by <xref
+        linkend="guc-log-disconnections"/>.
+       </para>
+
+       <para>
+        For the purposes of backwards compatibility, <literal>on</literal>,
+        <literal>off</literal>, <literal>true</literal>,
+        <literal>false</literal>, <literal>yes</literal>,
+        <literal>no</literal>, <literal>1</literal>, and <literal>0</literal>
+        are still supported. The positive values are equivalent to specifying
+        the <literal>receipt</literal>, <literal>authentication</literal>, and
+        <literal>authorization</literal> options.
+       </para>
+
+       <para>
         Only superusers and users with the appropriate <literal>SET</literal>
         privilege can change this parameter at session start,
         and it cannot be changed at all within a session.
-        The default is <literal>off</literal>.
        </para>
 
        <note>
 
 #include "postmaster/postmaster.h"
 #include "replication/walsender.h"
 #include "storage/ipc.h"
+#include "tcop/backend_startup.h"
 #include "utils/memutils.h"
 
 /*----------------------------------------------------------------
 /*
  * Sets the authenticated identity for the current user.  The provided string
  * will be stored into MyClientConnectionInfo, alongside the current HBA
- * method in use.  The ID will be logged if log_connections is enabled.
+ * method in use.  The ID will be logged if log_connections has the
+ * 'authentication' option specified.
  *
  * Auth methods should call this routine exactly once, as soon as the user is
  * successfully authenticated, even if they have reasons to know that
        MyClientConnectionInfo.authn_id = MemoryContextStrdup(TopMemoryContext, id);
        MyClientConnectionInfo.auth_method = port->hba->auth_method;
 
-       if (Log_connections)
+       if (log_connections & LOG_CONNECTION_AUTHENTICATION)
        {
                ereport(LOG,
                                errmsg("connection authenticated: identity=\"%s\" method=%s "
 #endif
        }
 
-       if (Log_connections && status == STATUS_OK &&
+       if ((log_connections & LOG_CONNECTION_AUTHENTICATION) &&
+               status == STATUS_OK &&
                !MyClientConnectionInfo.authn_id)
        {
                /*
 
 int                    AuthenticationTimeout = 60;
 
 bool           log_hostname;           /* for ps display and logging */
-bool           Log_connections = false;
 
 bool           enable_bonjour = false;
 char      *bonjour_name;
 
 #include "tcop/backend_startup.h"
 #include "tcop/tcopprot.h"
 #include "utils/builtins.h"
+#include "utils/guc_hooks.h"
 #include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/timeout.h"
+#include "utils/varlena.h"
 
 /* GUCs */
 bool           Trace_connection_negotiation = false;
+uint32         log_connections = 0;
+char      *log_connections_string = NULL;
 
 static void BackendInitialize(ClientSocket *client_sock, CAC_state cac);
 static int     ProcessSSLStartup(Port *port);
 static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
 static void process_startup_packet_die(SIGNAL_ARGS);
 static void StartupPacketTimeoutHandler(void);
+static bool validate_log_connections_options(List *elemlist, uint32 *flags);
 
 /*
  * Entry point for a new backend process.
        port->remote_host = MemoryContextStrdup(TopMemoryContext, remote_host);
        port->remote_port = MemoryContextStrdup(TopMemoryContext, remote_port);
 
-       /* And now we can issue the Log_connections message, if wanted */
-       if (Log_connections)
+       /* And now we can log that the connection was received, if enabled */
+       if (log_connections & LOG_CONNECTION_RECEIPT)
        {
                if (remote_port[0])
                        ereport(LOG,
 {
        _exit(1);
 }
+
+/*
+ * Helper for the log_connections GUC check hook.
+ *
+ * `elemlist` is a listified version of the string input passed to the
+ * log_connections GUC check hook, check_log_connections().
+ * check_log_connections() is responsible for cleaning up `elemlist`.
+ *
+ * validate_log_connections_options() returns false if an error was
+ * encountered and the GUC input could not be validated and true otherwise.
+ *
+ * `flags` returns the flags that should be stored in the log_connections GUC
+ * by its assign hook.
+ */
+static bool
+validate_log_connections_options(List *elemlist, uint32 *flags)
+{
+       ListCell   *l;
+       char       *item;
+
+       /*
+        * For backwards compatibility, we accept these tokens by themselves.
+        *
+        * Prior to PostgreSQL 18, log_connections was a boolean GUC that accepted
+        * any unambiguous substring of 'true', 'false', 'yes', 'no', 'on', and
+        * 'off'. Since log_connections became a list of strings in 18, we only
+        * accept complete option strings.
+        */
+       static const struct config_enum_entry compat_options[] = {
+               {"off", 0},
+               {"false", 0},
+               {"no", 0},
+               {"0", 0},
+               {"on", LOG_CONNECTION_ON},
+               {"true", LOG_CONNECTION_ON},
+               {"yes", LOG_CONNECTION_ON},
+               {"1", LOG_CONNECTION_ON},
+       };
+
+       *flags = 0;
+
+       /* If an empty string was passed, we're done */
+       if (list_length(elemlist) == 0)
+               return true;
+
+       /*
+        * Now check for the backwards compatibility options. They must always be
+        * specified on their own, so we error out if the first option is a
+        * backwards compatibility option and other options are also specified.
+        */
+       item = linitial(elemlist);
+
+       for (size_t i = 0; i < lengthof(compat_options); i++)
+       {
+               struct config_enum_entry option = compat_options[i];
+
+               if (pg_strcasecmp(item, option.name) != 0)
+                       continue;
+
+               if (list_length(elemlist) > 1)
+               {
+                       GUC_check_errdetail("Cannot specify log_connections option \"%s\" in a list with other options.",
+                                                               item);
+                       return false;
+               }
+
+               *flags = option.val;
+               return true;
+       }
+
+       /* Now check the aspect options. The empty string was already handled */
+       foreach(l, elemlist)
+       {
+               static const struct config_enum_entry options[] = {
+                       {"receipt", LOG_CONNECTION_RECEIPT},
+                       {"authentication", LOG_CONNECTION_AUTHENTICATION},
+                       {"authorization", LOG_CONNECTION_AUTHORIZATION},
+                       {"all", LOG_CONNECTION_ALL},
+               };
+
+               item = lfirst(l);
+               for (size_t i = 0; i < lengthof(options); i++)
+               {
+                       struct config_enum_entry option = options[i];
+
+                       if (pg_strcasecmp(item, option.name) == 0)
+                       {
+                               *flags |= option.val;
+                               goto next;
+                       }
+               }
+
+               GUC_check_errdetail("Invalid option \"%s\".", item);
+               return false;
+
+next:  ;
+       }
+
+       return true;
+}
+
+
+/*
+ * GUC check hook for log_connections
+ */
+bool
+check_log_connections(char **newval, void **extra, GucSource source)
+{
+       uint32          flags;
+       char       *rawstring;
+       List       *elemlist;
+       bool            success;
+
+       /* Need a modifiable copy of string */
+       rawstring = pstrdup(*newval);
+
+       if (!SplitIdentifierString(rawstring, ',', &elemlist))
+       {
+               GUC_check_errdetail("Invalid list syntax in parameter \"log_connections\".");
+               pfree(rawstring);
+               list_free(elemlist);
+               return false;
+       }
+
+       /* Validation logic is all in the helper */
+       success = validate_log_connections_options(elemlist, &flags);
+
+       /* Time for cleanup */
+       pfree(rawstring);
+       list_free(elemlist);
+
+       if (!success)
+               return false;
+
+       /*
+        * We succeeded, so allocate `extra` and save the flags there for use by
+        * assign_log_connections().
+        */
+       *extra = guc_malloc(ERROR, sizeof(int));
+       *((int *) *extra) = flags;
+
+       return true;
+}
+
+/*
+ * GUC assign hook for log_connections
+ */
+void
+assign_log_connections(const char *newval, void *extra)
+{
+       log_connections = *((int *) extra);
+}
 
 #include "storage/sinvaladt.h"
 #include "storage/smgr.h"
 #include "storage/sync.h"
+#include "tcop/backend_startup.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
         */
        disable_timeout(STATEMENT_TIMEOUT, false);
 
-       if (Log_connections)
+       if (log_connections & LOG_CONNECTION_AUTHORIZATION)
        {
                StringInfoData logmsg;
 
 
                true,
                NULL, NULL, NULL
        },
-       {
-               {"log_connections", PGC_SU_BACKEND, LOGGING_WHAT,
-                       gettext_noop("Logs each successful connection."),
-                       NULL
-               },
-               &Log_connections,
-               false,
-               NULL, NULL, NULL
-       },
        {
                {"trace_connection_negotiation", PGC_POSTMASTER, DEVELOPER_OPTIONS,
                        gettext_noop("Logs details of pre-authentication connection handshake."),
                NULL, NULL, NULL
        },
 
+       {
+               {"log_connections", PGC_SU_BACKEND, LOGGING_WHAT,
+                       gettext_noop("Logs specified aspects of connection establishment and setup."),
+                       NULL,
+                       GUC_LIST_INPUT
+               },
+               &log_connections_string,
+               "",
+               check_log_connections, assign_log_connections, NULL
+       },
+
+
        /* End-of-list marker */
        {
                {NULL, 0, 0, NULL, NULL}, NULL, NULL, NULL, NULL, NULL
 
 # require a server shutdown and restart to take effect.
 #
 # Any parameter can also be given as a command-line option to the server, e.g.,
-# "postgres -c log_connections=on".  Some parameters can be changed at run time
+# "postgres -c log_connections=all".  Some parameters can be changed at run time
 # with the "SET" SQL command.
 #
 # Memory units:  B  = bytes            Time units:  us  = microseconds
                                        # actions running at least this number
                                        # of milliseconds.
 #log_checkpoints = on
-#log_connections = off
+#log_connections = '' # log aspects of connection setup
+          # options include receipt, authentication, authorization,
+          # and all to log all of these aspects
 #log_disconnections = off
-#log_duration = off
+#log_duration = off # log statement duration
 #log_error_verbosity = default         # terse, default, or verbose messages
 #log_hostname = off
 #log_line_prefix = '%m [%p] '          # special values:
 
 extern PGDLLIMPORT bool ClientAuthInProgress;
 extern PGDLLIMPORT int PreAuthDelay;
 extern PGDLLIMPORT int AuthenticationTimeout;
-extern PGDLLIMPORT bool Log_connections;
 extern PGDLLIMPORT bool log_hostname;
 extern PGDLLIMPORT bool enable_bonjour;
 extern PGDLLIMPORT char *bonjour_name;
 
 
 /* GUCs */
 extern PGDLLIMPORT bool Trace_connection_negotiation;
+extern PGDLLIMPORT uint32 log_connections;
+extern PGDLLIMPORT char *log_connections_string;
 
 /*
  * CAC_state is passed from postmaster to the backend process, to indicate
        CAC_state       canAcceptConnections;
 } BackendStartupData;
 
+/*
+ * Granular control over which messages to log for the log_connections GUC.
+ *
+ * RECEIPT, AUTHENTICATION, and AUTHORIZATION are different aspects of
+ * connection establishment and backend setup for which we may emit a log
+ * message.
+ *
+ * ALL is a convenience alias equivalent to all of the above aspects.
+ *
+ * ON is backwards compatibility alias for the connection aspects that were
+ * logged in Postgres versions < 18.
+ */
+typedef enum LogConnectionOption
+{
+       LOG_CONNECTION_RECEIPT = (1 << 0),
+       LOG_CONNECTION_AUTHENTICATION = (1 << 1),
+       LOG_CONNECTION_AUTHORIZATION = (1 << 2),
+       LOG_CONNECTION_ON =
+               LOG_CONNECTION_RECEIPT |
+               LOG_CONNECTION_AUTHENTICATION |
+               LOG_CONNECTION_AUTHORIZATION,
+       LOG_CONNECTION_ALL =
+               LOG_CONNECTION_RECEIPT |
+               LOG_CONNECTION_AUTHENTICATION |
+               LOG_CONNECTION_AUTHORIZATION,
+} LogConnectionOption;
+
 extern void BackendMain(const void *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 #endif                                                 /* BACKEND_STARTUP_H */
 
 extern void assign_datestyle(const char *newval, void *extra);
 extern bool check_debug_io_direct(char **newval, void **extra, GucSource source);
 extern void assign_debug_io_direct(const char *newval, void *extra);
+extern bool check_log_connections(char **newval, void **extra, GucSource source);
+extern void assign_log_connections(const char *newval, void *extra);
 extern bool check_default_table_access_method(char **newval, void **extra,
                                                                                          GucSource source);
 extern bool check_default_tablespace(char **newval, void **extra,
 
 # - MD5-encrypted
 # - SCRAM-encrypted
 # This test can only run with Unix-domain sockets.
+#
+# There's also a few tests of the log_connections GUC here.
 
 use strict;
 use warnings FATAL => 'all';
 $node->append_conf('postgresql.conf', "log_connections = on\n");
 $node->start;
 
+# Test behavior of log_connections GUC
+#
+# There wasn't another test file where these tests obviously fit, and we don't
+# want to incur the cost of spinning up a new cluster just to test one GUC.
+
+# Make a database for the log_connections tests to avoid test fragility if
+# other tests are added to this file in the future
+$node->safe_psql('postgres', "CREATE DATABASE test_log_connections");
+
+$node->safe_psql('test_log_connections',
+       q[ALTER SYSTEM SET log_connections = receipt,authorization;
+                                  SELECT pg_reload_conf();]);
+
+$node->connect_ok('test_log_connections',
+       q(log_connections with subset of specified options logs only those aspects),
+       log_like => [
+               qr/connection received/,
+               qr/connection authorized: user=\S+ database=test_log_connections/,
+       ],
+       log_unlike => [
+               qr/connection authenticated/,
+       ],);
+
+$node->safe_psql('test_log_connections',
+       qq(ALTER SYSTEM SET log_connections = 'all'; SELECT pg_reload_conf();));
+
+$node->connect_ok('test_log_connections',
+       qq(log_connections 'all' logs all available connection aspects),
+       log_like => [
+               qr/connection received/,
+               qr/connection authenticated/,
+               qr/connection authorized: user=\S+ database=test_log_connections/,
+       ],);
+
+# Authentication tests
+
 # could fail in FIPS mode
 my $md5_works = ($node->psql('postgres', "select md5('')") == 0);
 
 
 LockViewRecurse_context
 LockWaitPolicy
 LockingClause
+LogConnectionOption
 LogOpts
 LogStmtLevel
 LogicalDecodeBeginCB