* Replace external KMS backend logic for AWS, Azure, and GCP with go-kms-wrapping
* Move kms client setup config into its own package for easier parsing
* Update kms integration flag naming
* Error if nil storage is passed to external KMS
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Signed-off-by: Daniel Weiße <dw@edgeless.systems>
So far the masterSecret was sent to the initial bootstrapper
on init/recovery. With this commit this information is encoded
in the kmsURI that is sent during init.
For recover, the communication with the recoveryserver is
changed. Before a streaming gRPC call was used to
exchanges UUID for measurementSecret and state disk key.
Now a standard gRPC is made that includes the same kmsURI &
storageURI that are sent during init.
