lib: Add phpdoc to class `AuthChain'

refs #5685

library/Icinga/Authentication/AuthChain.php

@@ -7,40 +7,81 @@ use Zend_Config;
 use Icinga\Logger\Logger;
 use Icinga\Exception\ConfigurationError;
 
+/**
+ * Iterate user backends created from config
+ */
 class AuthChain implements Iterator
 {
+    /**
+     * User backends configuration
+     *
+     * @var Zend_Config
+     */
     private $config;
 
+    /**
+     * The consecutive user backend while looping
+     *
+     * @var UserBackend
+     */
     private $currentBackend;
 
+    /**
+     * Create a new authentication chain from config
+     *
+     * @param Zend_Config $config User backends configuration
+     */
     public function __construct(Zend_Config $config)
     {
         $this->config = $config;
     }
 
+    /**
+     * Rewind the chain
+     */
     public function rewind()
     {
         $this->config->rewind();
+        $this->currentBackend = null;
     }
 
+    /**
+     * Return the current user backend
+     *
+     * @return UserBackend
+     */
     public function current()
     {
         return $this->currentBackend;
     }
 
+    /**
+     * Return the key of the current user backend config
+     *
+     * @return string
+     */
     public function key()
     {
         return $this->config->key();
     }
 
+    /**
+     * Move forward to the next user backend config
+     */
     public function next()
     {
         $this->config->next();
     }
 
+    /**
+     * Check if the current user backend is valid, i.e. it's enabled and the config's valid
+     *
+     * @return bool
+     */
     public function valid()
     {
         if (!$this->config->valid()) {
+            // Stop when there are no more backends to check
             return false;
         }
         $backendConfig = $this->config->current();