- `GET /api/v1/admin/domain_allows` lists allowed domains
- `GET /api/v1/admin/domain_allows/:id` shows one by ID
- `DELETE /api/v1/admin/domain_allows/:id` deletes a given domain from the list
of allowed domains
- `POST /api/v1/admin/domain_allows` to allow a new domain:
if that domain is already allowed, the existing DomainAllow will be returned
