Symfony provides some cool configuration features that would allow you to minimize your coding part .  In this tutorial i would explain how to configure security.yml to set credentials for a different users.

Create a class file named account.class.php under apps/frontend/lib folder with content .The class below checks weather the user is admin and sets his credential as ‘admin’ . Update the class file as your requirement .

class account
{
 public static function getLoginAdmin($username, $password)
 {
 // code to check for username and password in a particular table : ORM is doctrine
 $usr = Doctrine::getTable('TableName')
 ->createQuery('a')
 ->where('a.adminuser = ?',$username)
 ->andWhere('a.password = ?',$password)
 ->execute();

 $login_user = count($usr);

 if($login_user > 0)
 {
 sfContext::getInstance()->getUser()->setAuthenticated(true);
 sfContext::getInstance()->getUser()->addCredential('admin');

 return true;
 }
 else
 {
 return false;
 }
 }
 public static function LogoutSession()
 {
 sfContext::getInstance()->getUser()->setAuthenticated(false);
 sfContext::getInstance()->getUser()->clearCredentials();

 sfContext::getInstance()->getUser()->getAttributeHolder()->removeNamespace('admin');

 return true;
 }
}

And in login action file after receiving username and password call the library function as shown below

$login_flag = account::getLoginAdmin($this->username,$this->password);

and if $login_flag returns true you have successfully logged in else enter username or password is invalid .

You have done with the class file and action page . Now you need to configure security.yml .

Create a folder named config inside a module ( say for eg : under admin module ) with security.yml in it and paste the following code .

index:
is_secure: true
credentials: admin

Now admin module can be accessed only by one with ‘admin’ credential .

You can flush the credential as

$logout = account::LogoutSession();

You are done !