Fix that hidden elements are getting ovewritten when validating a form

This works by "disabling" hidden elements which causes the browser not
to submit them. Due to a bug in Zend we need to manually ensure that
Form::isValid does not overwrite the value of disabled elements with null.

fixes #7717

application/forms/Config/Authentication/AutologinBackendForm.php

@@ -66,7 +66,7 @@ class AutologinBackendForm extends Form
             'hidden',
             'backend',
             array(
-                'required'  => true,
+                'disabled'  => true,
                 'value'     => 'autologin'
             )
         );

application/forms/Config/Authentication/DbBackendForm.php

@@ -75,7 +75,7 @@ class DbBackendForm extends Form
             'hidden',
             'backend',
             array(
-                'required'  => true,
+                'disabled'  => true,
                 'value'     => 'db'
             )
         );

application/forms/Config/Authentication/LdapBackendForm.php

@@ -96,7 +96,7 @@ class LdapBackendForm extends Form
             'hidden',
             'backend',
             array(
-                'required'  => true,
+                'disabled'  => true,
                 'value'     => 'ldap'
             )
         );

library/Icinga/Web/Form.php

@@ -665,6 +665,14 @@ class Form extends Zend_Form
     public function isValidPartial(array $formData)
     {
         $this->create($formData);
+
+        // Ensure that disabled elements are not overwritten (http://www.zendframework.com/issues/browse/ZF-6909)
+        foreach ($this->getElements() as $name => $element) {
+            if ($element->getAttrib('disabled')) {
+                $formData[$name] = $element->getValue();
+            }
+        }
+
         return parent::isValidPartial($formData);
     }
 
@@ -678,6 +686,14 @@ class Form extends Zend_Form
     public function isValid($formData)
     {
         $this->create($formData);
+
+        // Ensure that disabled elements are not overwritten (http://www.zendframework.com/issues/browse/ZF-6909)
+        foreach ($this->getElements() as $name => $element) {
+            if ($element->getAttrib('disabled')) {
+                $formData[$name] = $element->getValue();
+            }
+        }
+
         return parent::isValid($formData);
     }