I have an SharePoint 2013 server that is up and running. I have also installed Workflow Manager 1.0 following the steps on Microsoft's website. At a certain point the instructions have you test Workflow manager by IE to the server on port 12290 and if you get some XML content back it's working. When I try that, I first get the prompt that there is a problem with the certificate. I click "continue" and then get "The website has declined to display this page". I've verified ports and things, and they are right. I've tried to ignore this and just go on to pairing Workflow and SharePoint, but that just gives me "The root of the certificate chain is not a trusted certificate authority." I generated the cert from my internal CA as per the Microsoft instructions. That is, I opened up the Certificates snap-in (on the workflow server) and requested a certificate for the computer.
The Workflow server is a separate server, not part of the farm.