code: func (c *Client) UpsertReverseTunnel(tunnel services.ReverseTunnel) error {
  	data, err := services.GetReverseTunnelMarshaler().MarshalReverseTunnel(tunnel)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	args := &upsertReverseTunnelRawReq{
  		ReverseTunnel: data,
  	}
  	_, err = c.PostJSON(c.Endpoint("reversetunnels"), args)
  	return trace.Wrap(err)
  }
docs: // UpsertReverseTunnel is used by admins to create a new reverse tunnel
  // to the remote proxy to bypass firewall restrictions