A non-signing node can be allowed to re-sign its new node keys following
key renewal/rotation (e.g. via `tailscale up --force-reauth`). To be
able to do this, node's TLK is written into WrappingPubkey field of the
initial SigDirect signature, signed by a signing node.
The intended use of this field implies that, for each WrappingPubkey, we
typically expect to have at most one active node with a signature
tracing back to that key. Multiple valid signatures referring to the
same WrappingPubkey can occur if a client's state has been cloned, but
it's something we explicitly discourage and don't support:
https://tailscale.com/s/clone
This change propagates rotation details (wrapping public key, a list
of previous node keys that have been rotated out) to netmap processing,
and adds tracking of obsolete node keys that, when found, will get
filtered out.
Updates tailscale/corp#19764
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
01847e0123