User Authentication ....

Model ...

public function validatePassword($password)
  {
	  	return $this->hashPassword($password)===$this->password;
	}
public function hashPassword($password)
	{
		return md5($password);
	}

UserIdentity.php

<?php

/**
 * UserIdentity represents the data needed to identity a user.
 * It contains the authentication method that checks if the provided
 * data can identity the user.
 */
class UserIdentity extends CUserIdentity
{
    private $_id;
    public function authenticate()
    {
        $username=strtolower($this->username);
  	$user=Users::model()->find('LOWER(username)=?',array($username));
		if($user===null)
		$this->errorCode=self::ERROR_USERNAME_INVALID;
		else if(!$user->validatePassword($this->password))
		$this->errorCode=self::ERROR_PASSWORD_INVALID;
		else
		{
		$this->_id=$user->user_id;
		$this->username=$user->username;
		$this->errorCode=self::ERROR_NONE;
		}
		return $this->errorCode==self::ERROR_NONE;

    }
 
    public function getId()
    {
        return $this->_id;
    }
}