For a few projects in the past, I had to find a way to make WordPress work with more than one domain. There are a couple plugins to do that, but they are outdated and/or don’t work well. So, I wrote this plugin.
Check this out: https://wordpress.org/plugins/multiple-domain/
Multiple Domain allows you having more than one domain in a single WordPress installation. This plugin doesn’t support more than one theme or advanced customizations for each domain. It’s only intended to enable constant navigation under many domains. For a more complex setup, there is WordPress Multisite (MU).
When there is more than one domain set in your host, all links and resources will point to the default domain. This is the default WordPress behavior. With Multiple Domain installed and properly configured, it’ll update all link on the fly. This way, the user navigation will be end-to-end under the same domain.
You can also set an optional base URL. If you want only a set of URL’s available under a given domain, you can use this restriction.
Photo credit: Roya Ann Miller