Unfortunately I don't think you will be able to disable SSL in Rancher v2.

As per Randcher documentation:

For security purposes, SSL (Secure Sockets Layer) is required when using Rancher. SSL secures all Rancher network communication, like when you login or interact with a cluster.

You can find there few ways to apply this certs:

• Default Rancher-generated Self-signed Certificate
• Bring Your Own Certificate, Self-signedlink
• Bring Your Own Certificate, Signed by a Recognized CA
• Let’s Encrypt Certificatelink

Inside this doc you have hyerlinks to further Rancher docs.

As Rancher by default deploying nginx controller you should also check Rancher docs about Nginx Controller.