Index: install/english.lang
===================================================================
--- install/english.lang	(revision 13140)
+++ install/english.lang	(working copy)
@@ -226,6 +226,7 @@
 			<PHRASE Label="la_config_ResizableFrames" Module="Core" Type="1">RnJhbWVzIGluIGFkbWluaXN0cmF0aXZlIGNvbnNvbGUgYXJlIHJlc2l6YWJsZQ==</PHRASE>
 			<PHRASE Label="la_config_Search_MinKeyword_Length" Module="Core" Type="1">TWluaW1hbCBTZWFyY2ggS2V5d29yZCBMZW5ndGg=</PHRASE>
 			<PHRASE Label="la_config_SessionBrowserSignatureCheck" Module="Core" Type="1">U2Vzc2lvbiBTZWN1cml0eSBDaGVjayBiYXNlZCBvbiBCcm93c2VyIFNpZ25hdHVyZQ==</PHRASE>
+			<PHRASE Label="la_config_SessionCookieDomains" Module="Core" Type="1">U2Vzc2lvbiBDb29raWUgRG9tYWlucyAoc2luZ2xlIGRvbWFpbiBwZXIgbGluZSk=</PHRASE>
 			<PHRASE Label="la_config_SessionIPAddressCheck" Module="Core" Type="1">U2Vzc2lvbiBTZWN1cml0eSBDaGVjayBiYXNlZCBvbiBJUA==</PHRASE>
 			<PHRASE Label="la_config_SiteNameSubTitle" Module="Core" Type="1">V2Vic2l0ZSBTdWJ0aXRsZQ==</PHRASE>
 			<PHRASE Label="la_config_site_zone" Module="Core" Type="1">VGltZSB6b25lIG9mIHRoZSBzaXRl</PHRASE>
Index: install/install_data.sql
===================================================================
--- install/install_data.sql	(revision 13151)
+++ install/install_data.sql	(working copy)
@@ -78,6 +78,8 @@
 INSERT INTO ConfigurationValues VALUES (DEFAULT, 'CookieSessions', '2', 'In-Portal', 'in-portal:configure_advanced');
 INSERT INTO ConfigurationAdmin VALUES ('SessionCookieName', 'la_section_SettingsSession', 'la_prompt_session_cookie_name', 'text', '', '', 20.02, 0, 1);
 INSERT INTO ConfigurationValues VALUES (DEFAULT, 'SessionCookieName', 'sid', 'In-Portal', 'in-portal:configure_advanced');
+INSERT INTO ConfigurationAdmin VALUES ('SessionCookieDomains', 'la_section_SettingsSession', 'la_config_SessionCookieDomains', 'textarea', '', 'rows="5" cols="40"', 20.021, 0, 0);
+INSERT INTO ConfigurationValues VALUES (DEFAULT, 'SessionCookieDomains', '', 'In-Portal', 'in-portal:configure_advanced');
 INSERT INTO ConfigurationAdmin VALUES ('KeepSessionOnBrowserClose', 'la_section_SettingsSession', 'la_config_KeepSessionOnBrowserClose', 'checkbox', '', '', 20.03, 0, 0);
 INSERT INTO ConfigurationValues VALUES (DEFAULT, 'KeepSessionOnBrowserClose', '0', 'In-Portal', 'in-portal:configure_advanced');
 INSERT INTO ConfigurationAdmin VALUES ('SessionBrowserSignatureCheck', 'la_section_SettingsSession', 'la_config_SessionBrowserSignatureCheck', 'checkbox', NULL, NULL, 20.04, 0, 1);
Index: install/upgrades.sql
===================================================================
--- install/upgrades.sql	(revision 13151)
+++ install/upgrades.sql	(working copy)
@@ -1650,3 +1650,6 @@
 
 DELETE FROM Phrase WHERE Phrase LIKE 'la_event_%';
 DELETE FROM PersistantSessionData WHERE VariableName = 'phrases_columns_.';
+
+INSERT INTO ConfigurationAdmin VALUES ('SessionCookieDomains', 'la_section_SettingsSession', 'la_config_SessionCookieDomains', 'textarea', '', 'rows="5" cols="40"', 20.021, 0, 0);
+INSERT INTO ConfigurationValues VALUES (DEFAULT, 'SessionCookieDomains', '', 'In-Portal', 'in-portal:configure_advanced');
Index: kernel/session/session.php
===================================================================
--- kernel/session/session.php	(revision 13128)
+++ kernel/session/session.php	(working copy)
@@ -536,9 +536,55 @@
 	 */
 	function SetCookieDomain($domain)
 	{
-		$this->CookieDomain = substr_count($domain, '.') ? '.'.ltrim($domain, '.') : false;
+		// 1. localhost or other like it without "." in domain name
+		if (!substr_count($domain, '.')) {
+			// don't use cookie domain at all
+			$this->CookieDomain = false;
+			return ;
+		}
+
+		// 2. match using predefined cookie domains from configuration
+		$cookie_domains = $this->Application->ConfigValue('SessionCookieDomains');
+
+		if ($cookie_domains) {
+			$cookie_domains = array_map('trim', explode("\n", $cookie_domains));
+
+			foreach ($cookie_domains as $cookie_domain) {
+				if (ltrim($cookie_domain, '.') == $domain) {
+					$this->CookieDomain = $cookie_domain; // as defined in configuration
+					return ;
+				}
+			}
+		}
+
+		// 3. only will execute, when none of domains were matched at previous step
+		$this->CookieDomain = $this->_autoGuessDomain($domain);
 	}
 
+	/**
+	 * Auto-guess cookie domain based on $_SERVER['HTTP_HOST']
+	 *
+	 * @param $domain
+	 * @return string
+	 */
+	function _autoGuessDomain($domain)
+	{
+		switch ( substr_count($domain, '.') ) {
+			case 2:
+				// 3rd level domain (3 parts)
+				return substr($domain, strpos($domain, '.')); // with leading "."
+				break;
+
+			case 1:
+				// 2rd level domain (2 parts)
+				return '.' . $domain; // with leading "."
+				break;
+		}
+
+		// more then 3rd level
+		return ltrim($domain, '.'); // without leading "."
+	}
+
 	function SetGETName($get_name)
 	{
 		$this->GETName = $get_name;
@@ -702,6 +748,13 @@
 			$this->Application->HttpQuery->Cookie[$name] = $value;
 		}
 
+		$old_style_domain = defined('IS_INSTALL') && IS_INSTALL ? '.' . SERVER_NAME : $this->_autoGuessDomain(SERVER_NAME);
+
+		if ($this->CookieDomain != $old_style_domain) {
+			// new style cookie domain -> delete old style cookie to prevent infinite redirect
+			setcookie($name, $value, adodb_mktime() - 3600, $this->CookiePath, $old_style_domain, $this->CookieSecure);
+		}
+
 		setcookie($name, $value, $expires, $this->CookiePath, $this->CookieDomain, $this->CookieSecure);
 	}
 
Index: kernel/utility/unit_config_reader.php
===================================================================
--- kernel/utility/unit_config_reader.php	(revision 13128)
+++ kernel/utility/unit_config_reader.php	(working copy)
@@ -81,6 +81,7 @@
 		$config_vars = Array (
 			'SessionTimeout',
 			'SessionCookieName',
+			'SessionCookieDomains',
 			'SessionBrowserSignatureCheck',
 			'SessionIPAddressCheck',
 			'CookieSessions',