diff --git a/framework/base/Model.php b/framework/base/Model.php
index 7818293..b9b5846 100644
--- a/framework/base/Model.php
+++ b/framework/base/Model.php
@@ -541,7 +541,7 @@ class Model extends Component implements \IteratorAggregate, \ArrayAccess
 	public function onUnsafeAttribute($name, $value)
 	{
 		if (YII_DEBUG) {
-			\Yii::info("Failed to set unsafe attribute '$name' in '" . get_class($this) . "'.", __CLASS__);
+			\Yii::info("Failed to set unsafe attribute '$name' in '" . get_class($this) . "'.", __METHOD__);
 		}
 	}
 
diff --git a/framework/base/Module.php b/framework/base/Module.php
index 6b82157..cf751c0 100644
--- a/framework/base/Module.php
+++ b/framework/base/Module.php
@@ -346,7 +346,7 @@ abstract class Module extends Component
 			if ($this->_modules[$id] instanceof Module) {
 				return $this->_modules[$id];
 			} elseif ($load) {
-				Yii::trace("Loading module: $id", __CLASS__);
+				Yii::trace("Loading module: $id", __METHOD__);
 				return $this->_modules[$id] = Yii::createObject($this->_modules[$id], $id, $this);
 			}
 		}
@@ -452,7 +452,7 @@ abstract class Module extends Component
 			if ($this->_components[$id] instanceof Component) {
 				return $this->_components[$id];
 			} elseif ($load) {
-				Yii::trace("Loading component: $id", __CLASS__);
+				Yii::trace("Loading component: $id", __METHOD__);
 				return $this->_components[$id] = Yii::createObject($this->_components[$id]);
 			}
 		}
diff --git a/framework/db/Command.php b/framework/db/Command.php
index ecd3674..a30aa14 100644
--- a/framework/db/Command.php
+++ b/framework/db/Command.php
@@ -134,7 +134,7 @@ class Command extends \yii\base\Component
 			try {
 				$this->pdoStatement = $this->db->pdo->prepare($sql);
 			} catch (\Exception $e) {
-				Yii::error($e->getMessage() . "\nFailed to prepare SQL: $sql", __CLASS__);
+				Yii::error($e->getMessage() . "\nFailed to prepare SQL: $sql", __METHOD__);
 				$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
 				throw new Exception($e->getMessage(), $errorInfo, (int)$e->getCode());
 			}
@@ -266,15 +266,16 @@ class Command extends \yii\base\Component
 			$paramLog = "\nParameters: " . var_export($this->_params, true);
 		}
 
-		Yii::trace("Executing SQL: {$sql}{$paramLog}", __CLASS__);
+		Yii::trace("Executing SQL: {$sql}{$paramLog}", __METHOD__);
 
 		if ($sql == '') {
 			return 0;
 		}
 
 		try {
+			$token = "SQL: $sql";
 			if ($this->db->enableProfiling) {
-				Yii::beginProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::beginProfile($token, __METHOD__);
 			}
 
 			$this->prepare();
@@ -282,16 +283,16 @@ class Command extends \yii\base\Component
 			$n = $this->pdoStatement->rowCount();
 
 			if ($this->db->enableProfiling) {
-				Yii::endProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::endProfile($token, __METHOD__);
 			}
 			return $n;
 		} catch (\Exception $e) {
 			if ($this->db->enableProfiling) {
-				Yii::endProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::endProfile($token, __METHOD__);
 			}
 			$message = $e->getMessage();
 
-			Yii::error("$message\nFailed to execute SQL: {$sql}{$paramLog}", __CLASS__);
+			Yii::error("$message\nFailed to execute SQL: {$sql}{$paramLog}", __METHOD__);
 
 			$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
 			throw new Exception($message, $errorInfo, (int)$e->getCode());
@@ -383,7 +384,7 @@ class Command extends \yii\base\Component
 			$paramLog = "\nParameters: " . var_export($this->_params, true);
 		}
 
-		Yii::trace("Querying SQL: {$sql}{$paramLog}", __CLASS__);
+		Yii::trace("Querying SQL: {$sql}{$paramLog}", __METHOD__);
 
 		/** @var $cache \yii\caching\Cache */
 		if ($db->enableQueryCache && $method !== '') {
@@ -399,14 +400,15 @@ class Command extends \yii\base\Component
 				$paramLog,
 			));
 			if (($result = $cache->get($cacheKey)) !== false) {
-				Yii::trace('Query result served from cache', __CLASS__);
+				Yii::trace('Query result served from cache', __METHOD__);
 				return $result;
 			}
 		}
 
 		try {
+			$token = "SQL: $sql";
 			if ($db->enableProfiling) {
-				Yii::beginProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::beginProfile($token, __METHOD__);
 			}
 
 			$this->prepare();
@@ -423,21 +425,21 @@ class Command extends \yii\base\Component
 			}
 
 			if ($db->enableProfiling) {
-				Yii::endProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::endProfile($token, __METHOD__);
 			}
 
 			if (isset($cache, $cacheKey) && $cache instanceof Cache) {
 				$cache->set($cacheKey, $result, $db->queryCacheDuration, $db->queryCacheDependency);
-				Yii::trace('Saved query result in cache', __CLASS__);
+				Yii::trace('Saved query result in cache', __METHOD__);
 			}
 
 			return $result;
 		} catch (\Exception $e) {
 			if ($db->enableProfiling) {
-				Yii::endProfile(__METHOD__ . "($sql)", __CLASS__);
+				Yii::endProfile($token, __METHOD__);
 			}
 			$message = $e->getMessage();
-			Yii::error("$message\nCommand::$method() failed: {$sql}{$paramLog}", __CLASS__);
+			Yii::error("$message\nCommand::$method() failed: {$sql}{$paramLog}", __METHOD__);
 			$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
 			throw new Exception($message, $errorInfo, (int)$e->getCode());
 		}
diff --git a/framework/db/Connection.php b/framework/db/Connection.php
index 59e8422..e84970b 100644
--- a/framework/db/Connection.php
+++ b/framework/db/Connection.php
@@ -324,12 +324,12 @@ class Connection extends Component
 				throw new InvalidConfigException('Connection::dsn cannot be empty.');
 			}
 			try {
-				\Yii::trace('Opening DB connection: ' . $this->dsn, __CLASS__);
+				\Yii::trace('Opening DB connection: ' . $this->dsn, __METHOD__);
 				$this->pdo = $this->createPdoInstance();
 				$this->initConnection();
 			}
 			catch (\PDOException $e) {
-				\Yii::error("Failed to open DB connection ({$this->dsn}): " . $e->getMessage(), __CLASS__);
+				\Yii::error("Failed to open DB connection ({$this->dsn}): " . $e->getMessage(), __METHOD__);
 				$message = YII_DEBUG ? 'Failed to open DB connection: ' . $e->getMessage() : 'Failed to open DB connection.';
 				throw new Exception($message, $e->errorInfo, (int)$e->getCode());
 			}
@@ -343,7 +343,7 @@ class Connection extends Component
 	public function close()
 	{
 		if ($this->pdo !== null) {
-			\Yii::trace('Closing DB connection: ' . $this->dsn, __CLASS__);
+			\Yii::trace('Closing DB connection: ' . $this->dsn, __METHOD__);
 			$this->pdo = null;
 			$this->_schema = null;
 			$this->_transaction = null;
diff --git a/framework/db/Transaction.php b/framework/db/Transaction.php
index 177d2cb..d66c38e 100644
--- a/framework/db/Transaction.php
+++ b/framework/db/Transaction.php
@@ -66,7 +66,7 @@ class Transaction extends \yii\base\Object
 			if ($this->db === null) {
 				throw new InvalidConfigException('Transaction::db must be set.');
 			}
-			\Yii::trace('Starting transaction', __CLASS__);
+			\Yii::trace('Starting transaction', __METHOD__);
 			$this->db->open();
 			$this->db->pdo->beginTransaction();
 			$this->_active = true;
@@ -80,7 +80,7 @@ class Transaction extends \yii\base\Object
 	public function commit()
 	{
 		if ($this->_active && $this->db && $this->db->isActive) {
-			\Yii::trace('Committing transaction', __CLASS__);
+			\Yii::trace('Committing transaction', __METHOD__);
 			$this->db->pdo->commit();
 			$this->_active = false;
 		} else {
@@ -95,7 +95,7 @@ class Transaction extends \yii\base\Object
 	public function rollback()
 	{
 		if ($this->_active && $this->db && $this->db->isActive) {
-			\Yii::trace('Rolling back transaction', __CLASS__);
+			\Yii::trace('Rolling back transaction', __METHOD__);
 			$this->db->pdo->rollBack();
 			$this->_active = false;
 		} else {
diff --git a/framework/i18n/PhpMessageSource.php b/framework/i18n/PhpMessageSource.php
index 6b12353..1ada44a 100644
--- a/framework/i18n/PhpMessageSource.php
+++ b/framework/i18n/PhpMessageSource.php
@@ -72,7 +72,7 @@ class PhpMessageSource extends MessageSource
 			}
 			return $messages;
 		} else {
-			Yii::error("The message file for category '$category' does not exist: $messageFile", __CLASS__);
+			Yii::error("The message file for category '$category' does not exist: $messageFile", __METHOD__);
 			return array();
 		}
 	}
diff --git a/framework/web/Identity.php b/framework/web/Identity.php
index 4668337..805d3d4 100644
--- a/framework/web/Identity.php
+++ b/framework/web/Identity.php
@@ -16,15 +16,14 @@ interface Identity
 {
 	/**
 	 * Returns an ID that can uniquely identify a user identity.
-	 * The returned ID can be a string, an integer, or any serializable data.
-	 * @return mixed an ID that uniquely identifies a user identity.
+	 * @return string|integer an ID that uniquely identifies a user identity.
 	 */
 	public function getId();
 	/**
 	 * Returns a key that can be used to check the validity of a given identity ID.
 	 * The space of such keys should be big and random enough to defeat potential identity attacks.
 	 * The returned key can be a string, an integer, or any serializable data.
-	 * @return mixed a key that is used to check the validity of a given identity ID.
+	 * @return string a key that is used to check the validity of a given identity ID.
 	 * @see validateAuthKey()
 	 */
 	public function getAuthKey();
@@ -37,7 +36,7 @@ interface Identity
 	public function validateAuthKey($authKey);
 	/**
 	 * Finds an identity by the given ID.
-	 * @param mixed $id the ID to be looked for
+	 * @param string|integer $id the ID to be looked for
 	 * @return Identity the identity object that matches the given ID.
 	 * Null should be returned if such an identity cannot be found.
 	 */
diff --git a/framework/web/Session.php b/framework/web/Session.php
index c289db2..3e0f599 100644
--- a/framework/web/Session.php
+++ b/framework/web/Session.php
@@ -117,7 +117,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
 				$this->_opened = false;
 				$error = error_get_last();
 				$message = isset($error['message']) ? $error['message'] : 'Failed to start session.';
-				Yii::error($message, __CLASS__);
+				Yii::error($message, __METHOD__);
 			} else {
 				$this->_opened = true;
 				$this->updateFlashCounters();
diff --git a/framework/web/User.php b/framework/web/User.php
index 2326a10..74b5f18 100644
--- a/framework/web/User.php
+++ b/framework/web/User.php
@@ -90,6 +90,9 @@ class User extends Component
 	{
 		parent::init();
 
+		if ($this->identityClass === null) {
+			throw new InvalidConfigException('User::identityClass must be set.');
+		}
 		if ($this->enableAutoLogin && !isset($this->identityCookie['name'])) {
 			throw new InvalidConfigException('User::identityCookie must contain the "name" element.');
 		}
@@ -179,7 +182,13 @@ class User extends Component
 				/** @var $class Identity */
 				$class = $this->identityClass;
 				$identity = $class::findIdentity($id);
-				if ($identity !== null && $identity->validateAuthKey($authKey) && $this->beforeLogin($identity, true)) {
+				if ($identity === null || !$identity->validateAuthKey($authKey)) {
+					if ($identity !== null) {
+						Yii::warning("Invalid auth key attempted for user '$id': $authKey", __METHOD__);
+					}
+					return;
+				}
+				if ($this->beforeLogin($identity, true)) {
 					$this->switchIdentity($identity);
 					if ($this->autoRenewCookie) {
 						$this->saveIdentityCookie($identity, $duration);