Injecting SSH-keys automatically on host creation (Openstack)

Yesterday, I tried to rollout RancherOS in our Openstack environmen. For the deployment I used the latest rancheros-openstack.img image. In comparison with CentOS and Ubuntu it seems that cloud-init works a little bit different and it was not possible for me to inject ssh-keys automatically. The only way was the described option with the hardcoded key in the cloud-config.yml file. Is there another way available for openstack environments to enable automatic key injection to RancherOS? Have I overlooked anything?

Thanks for your support