When you think about it, DNS configuration is actually a very rudimentary NoSQL database. You can view and modify it at any time quite easily through your domain provider’s website, and you can view each “record” just like a row in a database table.
Many services use DNS TXT records to verify domain ownership. You would essentially add or modify a TXT record to store a key/value pair, which the service will then query.
Why? It’s super fast and costs $0.50 + $0.40 per million queries.