Security schemes regularly in use on cloud

I've been looking into how connections are managed in the cloud, in order to better understand the threats users and their deployments may face.

The most important and common ones in use seem to be either SSH, to connect directly to an instance, or between two instances, or something using key managers to look after multiple connections using PKI, something like Kerberos for instance.

Are there any other important ones I've missed? I've been looking but haven't found anything which lists specific schemes and this is what I've come up with.