Embedding an Apex application within another webpage

Requirement

You need a quick and easy way to embed an entire application within another page.

Solution

In the setting of your apex application, you need to adjust the security settings to allow the application to be embedded.

1. Click on Application Builder
2. Click the name of the application you want to enable to open it
3. On the title bar where your application name appears, click on Edit Application Properties (button to the right)
4. Toward the top, locate the link for Security and click it
5. Scroll down to the Browser Security section or click on the tab labeled Browser Security
6. Assuming it says Deny, change it to Allow or Allow from same origin
7. Press Apply Changes

Sample code for calling your app (This is Python)..

<div class="embed-responsive embed-responsive-16by9">

<iframe class="embed-responsive-item" src="https://apex.oracle.com/pls/apex/(blahblah)" allowfullscreen></iframe>

</div>

NOTE: If you are using Apex 20 or later you need to be aware of the URL that you are using. 
I use p? notation, which means I have to disable URL friendly syntax in the application settings.

Result 

 

Acknowledgment 

https://stackoverflow.com/questions/28452000/how-to-embed-an-apex-website-on-my-html-website