https web server I would like to protect with WAF

I have an existing https web server, that I would like to try to protect with WAF. I'm unsure if I can keep the existing cert keys, and just import them somehow for use with WAF. I don't want to rekey by regenerating one for the ASG, in case the WAF behaves or doesn't support the https application properly.

How can I import the existing keyed cert into the ASG for use with WAF? I would also need to get the intermediate cert on there also. I can export into Tomcat, or Apache, and unsure which the ASG accepts.

Any input is appreciated. Thanks

Brian