This is one of the most common error when it comes to make calls to https url’s with <cfhttp. A lot of articles are out there explaining how to install SSL certificate with keytool. But again its not very easy for everyone to understand. 

Best way to do it is using certman (CF admin) plugin, which was available on https://certman.riaforge.org/ but since its been taken down it was no where to be found. I recently found it in https://github.com/cfmaniac GIT repo and forked it to https://github.com/LucidSolutions/CF-CertMan so that I have safe for future usages.

Download SSL certificate

1. We can use Firefox to view and export the certificate.
2. Browse the url in FF and then click on the lock icon
3. Click on Show Connection details and then More Information
4. You will see a button View Certificate, Click that and there will be an option to download the PEM (cert) file

Installing CertMan

1. Depending on the version you can find install instruction file in the repo e.g. “https://github.com/LucidSolutions/CF-CertMan/blob/master/CF-10/install/install.txt”
2. Follow the instructions and then restart CF server.
3. You will see a new menu “SSL Certificates” -> “Certificate Management”
4. You can click on “Certificate Management” and then “Add a New Certificate” button

Note :-  I have installed CF 10 version on CF 11 and it works and as per https://github.com/cfmaniac/CF-CertMan/issues/7 it works on CF 2016 and CF 2018 too.