Mono has its own certificate store, and by default, trusts nothing. You can follow these steps to install some default certificates, or install your own from a .PEM file.

1. Download the CA certificate bundle.
2. From a PASE shell with Mono in $PATH, run cert-sync --user cacert.pem, or point to another .PEM file you want to install from. Alternatively, if you run from a user with *ALLOBJ, you can omit the --user flag to install certificates for all users.)