在Codeigniter上连接特定代码

I am new with CodeIgniter, how to display this url below using concatenate on codeigniter:

<iframe style="border: 0;" src="http://domain.com.ABC123.html" width="800" height="450" frameborder="0" allowfullscreen="allowfullscreen"></iframe>

• URL : http://domain.com.ABC123.html
• KEY : ABC123 (Stored in database and there will be different code for each users)

I need to concatenate the KEY only for each active users.