copy# 1 · trust the CDN signing key
curl -fsSL https://cdn.thern.io/keys/thern-cdn-keyring.gpg \
  | sudo tee /usr/share/keyrings/thern-cdn-keyring.gpg >/dev/null

# 2 · add the repository
echo "deb [signed-by=/usr/share/keyrings/thern-cdn-keyring.gpg] \
  https://cdn.thern.io/deb stable main" \
  | sudo tee /etc/apt/sources.list.d/thern-cdn.list

# 3 · install
sudo apt update && sudo apt install wainhold-frontier