I embedded my OsClass page into a page on my site by calling it in an iframe statement.  This lets me retain my webpage header & footer, but still use the OSClass page within it.  It loads fine and I can browse items that have been posted, but I'm unable to login to OsClass.  Here's the code I added to my site:
 <iframe src="<URL of my website>/OSClass/" width=900px height=1400px frameborder="0" >
            </iframe>

If I access <URL of my website>/OSClass/ directly, I can login to OSClass, so I know the site and my login are working.

Anyone know why I can't login to OsClass when accessed in this manner?

Tried <embed> and <object>, but am getting the same result.  Login page comes up, I enter valid credentials, but am not granted access.

This is quite common but I would say this is browser security.
We also used to run demo sites in iframe until there were many complaints that front/backoffice login does not work.

Maybe check this:
https://stackoverflow.com/questions/63398679/sso-login-not-working-in-iframe-after-chrome-update

Cross-domain login may not work

Any suggestions on a better way of embedding the OSClass content within my page?

Any suggestions on a better way of embedding the OSClass content within my page?

Is there another way to link to the OSClass content from within my existing page?  I'd rather not have OSClass open up in a separate tab or browser outside of my existing website.

Iframe is for that.
Other methods usually does not work well.

Proposals sent before in that link

When I changed the URL to use https:// instead of http:// in the Embed statement, everything worked as expected.

I do not think it is guaranteed, but it should at least work if page and iframe source use same domain