This commit introduces the HTTP interface for the dynamic K8s node
provisioner. It will serve as the main communication point between the
ephemeral nodes in the cloud, sharing the keys and tokens they require
in order to join the Kubernetes cluster.
The initial functionality is simply an Amazon SNS notification receiver.
SNS notifications will be used to manage the lifecycle of the dynamic
nodes.
For now, the notification receiver handles subscription confirmation
messages by following the link provided to confirm the subscription.
All other messages are simply written to the filesystem; these will be
used to implement and test future functionality.
In order to prevent arbitrary clients from using the provisioner to
retrieve WireGuard keys and Kubernetes bootstrap tokens, access to those
resources *must* be restricted to the EC2 machines created by the
Kubernetes Cloud Autoscaler. The key to the authentication process will
be SNS notifications from AWS to indicate when new EC2 instances are
created; everything that the provisioner does will be associated with an
instance it discovered through an SNS notification.
SNS messages are signed using PKCS#1 v1.5 RSA-SHA1, with a public key
distributed in an X.509 certificate. To ensure that messages received
are indeed from AWS, the provisioner will need to verify those
signatures. Messages with missing or invalid signatures will be
considered unsafe and ignored.
The `model::sns` module includes the data structures that represent SNS
messages. The `sns::sig` module includes the primitive operations for
implementing signature verification.
Dustin