Carrd is a platform for creating no-code landing pages ( https://carrd.co/ ). The premium features allow you to add code and iframes. In fact, I'd like to make a landing page & share it with 20 people on my team only. Carrd lets you set a login and password (but it would be the same for everyone). But I'd like to control access? Is this possible with OnzAuth? Is it really secure?

Did you mean logging in to Carrd's admin portal? I don't think we can override that feature.

No, I want to create a site with carrds. Put it online, and restrict access to it with OnzAuth. That way, only the people I've authorized will be able to access the site.

We are not familiar with Carrds, but if you can access the header html/javascript of the page, you should be able to do it, similar to our Webflow guide. But if you wish to override existing login provided by Carrd, it can be done but you might need a coder to override it with code, like with our Wordpress plugin which you can reference via the open sourced repository. Hope it helps.