Thanks to your pointer, I figured out the solution.
I used the FAQ link posted in my question to download a ca-certificates.crt file that I passed to --ca-cert parameter of rclone config. Everything worked fine but now I have to give the --ca-cert every time I use a rclone command. Is there anyway I could add this to the config file as a default, or do I have to use some shell tricks like aliasing to make this simple?
I don't have root privileges, so I cannot save the file in the default location (/etc/ssl/certs/).