puppet module install failing with SSL error on Puppet 5.3

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I'm stuck -- Our site has a self-signed certificate they inject. i'm pretty sure I have my CA certificates set up correctly on my Redhat Linux box to handle them (i.e. other software works), but I can't install any puppet modules. This is all I get:

# puppet module install puppetlabs-docker --verbose --version 1.0.5
Notice: Preparing to install into /etc/puppetlabs/code/environments/production/modules ...
Notice: Downloading from https://forgeapi.puppet.com ...
Error: Could not connect via HTTPS to https://forgeapi.puppet.com
  Unable to verify the SSL certificate
    The certificate may not be signed by a valid CA
    The CA bundle included with OpenSSL may not be valid or up to date

Is there something unique about the way that puppet deals with certificates in this situation?

Thanks, John