GET to set the ``csrftoken`` cookie before unsafe requests from the SPA.

GET /api/auth/csrf/
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "detail": "ok",
    "csrfToken": "79Bz6484fqYNKiWfBOCSZVRL4aa2ZwWNH2CRQ2ckSDeoV1m2sePWWfRjoNzM5T7s"
}