DNS Providers

$ CLOUDFLARE_EMAIL=you@example.com \
  CLOUDFLARE_API_KEY=b9841238feb177a84330febba8a83208921177bffe733 \
  lego --dns cloudflare --domains www.example.com --email you@example.com run

$ cat /the/path/to/my/key
b9841238feb177a84330febba8a83208921177bffe733

$ cat /the/path/to/my/email
you@example.com

$ CLOUDFLARE_EMAIL_FILE=/the/path/to/my/email \
  CLOUDFLARE_API_KEY_FILE=/the/path/to/my/key \
  lego --dns cloudflare --domains www.example.com --email you@example.com run