Wizard: show LDAP connection settings discovery failure reasons

refs #2865

library/Icinga/Protocol/Ldap/Discovery.php

@@ -81,6 +81,16 @@ class Discovery
         return $this->connection->discoverySuccessful();
     }
 
+    /**
+     * Why the discovery failed
+     *
+     * @return \Exception|null
+     */
+    public function getError()
+    {
+        return $this->connection->getDiscoveryError();
+    }
+
     /**
      * Discover LDAP servers on the given domain
      *

library/Icinga/Protocol/Ldap/LdapConnection.php

@@ -153,6 +153,13 @@ class LdapConnection implements Selectable, Inspectable
      */
     protected $discoverySuccess;
 
+    /**
+     * The cause of the discovery's failure
+     *
+     * @var Exception|null
+     */
+    private $discoveryError;
+
     /**
      * Whether the current connection is encrypted
      *
@@ -250,11 +257,13 @@ class LdapConnection implements Selectable, Inspectable
             try {
                 $this->capabilities = LdapCapabilities::discoverCapabilities($this);
                 $this->discoverySuccess = true;
+                $this->discoveryError = null;
             } catch (LdapException $e) {
                 Logger::debug($e);
                 Logger::warning('LADP discovery failed, assuming default LDAP capabilities.');
                 $this->capabilities = new LdapCapabilities(); // create empty default capabilities
                 $this->discoverySuccess = false;
+                $this->discoveryError = $e;
             }
         }
 
@@ -275,6 +284,16 @@ class LdapConnection implements Selectable, Inspectable
         return $this->discoverySuccess;
     }
 
+    /**
+     * Get discovery error if any
+     *
+     * @return Exception|null
+     */
+    public function getDiscoveryError()
+    {
+        return $this->discoveryError;
+    }
+
     /**
      * Return whether the current connection is encrypted
      *

modules/setup/application/forms/LdapDiscoveryPage.php

@@ -74,6 +74,8 @@ class LdapDiscoveryPage extends Form
                 $this->discovery = Discovery::discoverDomain($data['domain']);
                 if ($this->discovery->isSuccess()) {
                     return true;
+                } else {
+                    $this->error($this->discovery->getError()->getMessage());
                 }
             } catch (Exception $e) {
                 $this->error(sprintf(