Create application/Models/DbTable/Users.php

<?php
class Model_DbTable_Users extends Zend_Db_Table_Abstract
{
    protected $_name = 'users';
    public function findCredentials($username, $pwd)
    {
        $select = $this->select()->where('username = ?', $username)
            ->where('password = ?', $this->hashPassword($pwd));
        $row = $this->fetchRow($select);
        if($row) {
            return $row;
        }
        return false;
    }
    protected function hashPassword($pwd)
    {
        return md5($pwd);
    }
}

Create application/Models/DbTable/Comments.php

<?php
class Model_DbTable_Comments extends Zend_Db_Table_Abstract
{
    protected $_name = 'comments';
    public function getComments( $postid ) 
    {
        $result = $this->fetchAll( "post_id = '$postid'"  );
        return $result->toArray();
    }
    public function saveComment( $commentForm )
    {
        $data = array('post_id' => $commentForm['id'] ,
                'Description' => $commentForm['comment'],
                'Name' => $commentForm['name'],
                'Email' => $commentForm['email'],
                'Webpage' => $commentForm['webpage'] );
        $this->insert($data);
    }
}

 Now lets create a login form in /application/forms/Login.php directory . 

<?php
class Form_Login extends Zend_Form
{
    public function __construct()
    {
        parent::__construct($options);
        $this->setName('UserLogin');
        $username = new Zend_Form_Element_Text('username');
        $username->setLabel('User Name')
                ->setRequired(true)
                ->addFilter('StripTags')
                ->addFilter('StringTrim')
                ->addValidator('NotEmpty');
        $pass = new Zend_Form_Element_Password('pass');
        $pass->setLabel('Password')
                ->setRequired(true)
                ->addFilter('StripTags')
                ->addFilter('StringTrim')
                ->addValidator('NotEmpty');
        $submit = new Zend_Form_Element_Submit('submit');
        $redirect = new Zend_Form_Element_Hidden('redirect');
        $submit->setAttrib('id', 'submitbutton');
        $this->addElements( array ( $username, $pass, $submit));
    }
}

Create a form for posting and commenting

application/forms/posts.php

<?php
class Form_Post extends Zend_Form
{
    public function __construct()
    {
        parent::__construct($options);
        $this->setName('Posts');
        $id = new Zend_Form_Element_Hidden('id');
        $title = new Zend_Form_Element_Text('Title');
        $title->setLabel('Title')
                ->setRequired(true)
                ->addFilter('StripTags')
                ->addFilter('StringTrim')
                ->addValidator('NotEmpty');
        $description = new Zend_Form_Element_Textarea('Description');
        $description->setLabel('Description')
                ->setRequired(true)
                ->setAttrib('rows',20)
                ->setAttrib('cols',50)
                ->addFilter('StripTags')
                ->addFilter('StringTrim')
                ->addValidator('NotEmpty');
        $submit = new Zend_Form_Element_Submit('submit');
        $submit->setAttrib('id', 'submitbutton');
        $this->addElements( array( $id, $title, $description, $submit ));
    }
}

Create a comments form application/forms/Comments.php for adding comments

<?php
class Form_Comments extends Zend_Form
{
    public function __construct()
    {
        $acl = new Model_Acl();
        $identity = Zend_Auth::getInstance()->getIdentity();
        /*
        * Check whether they have permission to add comments
        */
        if( Zend_Auth::getInstance()->hasIdentity()
        && $acl->isAllowed( $identity['role'] ,'comments','add') ) {
            parent::__construct($options);
            $this->setName('Comments');
            $id = new Zend_Form_Element_Hidden('id');
            $name = new Zend_Form_Element_Text('name');
            $name->setLabel('Your Name')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');
            $email = new Zend_Form_Element_Text('email');
            $email->setLabel('Email')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');
            $webpage = new Zend_Form_Element_Text('webpage');
            $webpage->setLabel('Webpage')
            ->setRequired(true)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');
            $comment = new Zend_Form_Element_Textarea('comment');
            $comment->setLabel('Comments')
            ->setRequired(true)
            ->setAttrib('rows',7)
            ->setAttrib('cols',30)
            ->addFilter('StripTags')
            ->addFilter('StringTrim')
            ->addValidator('NotEmpty');
            $submit = new Zend_Form_Element_Submit('submit');
            $submit->setAttrib('id', 'submitbutton');
            $this->addElements( array ($id, $name, $email, $webpage, $comment, $submit));
        }
    }
}

Create application/Models/Acl.php

<?php
class Model_Acl extends Zend_Acl 
{
    public function __construct() 
    {
        /*
         *  Add a new role called "guest"
         *  Guest can view contents of the site 
         */
        $this->addRole(new Zend_Acl_Role('guest'));
        /* 
         * Add a role called user, which inherits from guest
         * Users can post comments in site
         */
        $this->addRole(new Zend_Acl_Role('user'), 'guest');
        /* 
         * Add a role called blogger, which inherits from user
         * Bloggers can post contents
         */
        $this->addRole(new Zend_Acl_Role('blogger'), 'user');
        /*
         * Add a role for admin which inherits blogger
         * With every privilages
         */
        $this->addRole(new Zend_Acl_Role('admin'), 'blogger');
        //Add a resource called posts
        $this->add(new Zend_Acl_Resource('posts'));
        //Add a resource called edit, which inherits posts
        //$this->add(new Zend_Acl_Resource('edit'), 'posts');
        //Add a resource called edit
        //$this->add(new Zend_Acl_Resource('add'), 'posts');
        //Finally, we want to allow guests to view pages
        $this->allow('guest', 'posts', 'view');
        // Bloggers can add, edit posts
        $this->allow('blogger', 'posts', 'edit');
        $this->allow('blogger', 'posts', 'add');
    }
}

Create application/Models/AuthAdapter.php

<?php
class Model_AuthAdapter implements Zend_Auth_Adapter_Interface
{
    protected $username;
    protected $password;
    protected $user;
    public function __construct($username, $password) {
        $this->username = $username;
        $this->password = $password;
        $this->user = new Model_DbTable_Users();
    }
    public function authenticate()
    {
        $match = $this->user->findCredentials($this->username, $this->password);
        //var_dump($match);
        if(!$match) {
            $result = new Zend_Auth_Result(Zend_Auth_Result::FAILURE_CREDENTIAL_INVALID, null);
        } else {
            $user = current($match);
            $result = new Zend_Auth_Result(Zend_Auth_Result::SUCCESS, $user);
        }
        return $result;
    }
}

Create application/views/helpers/BaseUrl.php

<?php
class Zend_View_Helper_BaseUrl {
    function baseUrl() {
        $fc = Zend_Controller_Front::getInstance();
        return $fc->getBaseUrl();
    }
}
?>

Create application/views/helpers/LinkTo.php

<?php
class Zend_View_Helper_LinkTo
{
    protected static $baseUrl = null;
    public function linkTo($path)
    {
        if (self::$baseUrl === null) {
            $request = Zend_Controller_Front::getInstance()->getRequest();
            $root = '/' . trim($request->getBaseUrl(), '/');
            if ($root == '/') {
                $root = '';
            }
            self::$baseUrl = $root . '/';
        }
        return self::$baseUrl . ltrim($path, '/');
    }
}