Requesting NIST NVD API key:

NVD API: keys, documentation, and request limits!
To better serve its growing user base, the NVD is announcing the availability of API keys. Users who request and activate a key may include it as a parameter of their request’s URL string. Along with the release of API Keys, the NVD will be unveiling new API documentation and information to help new developers get started with the NVD API. Beginning six months after the release of the API keys, users transmitting requests without a key will see a reduction in the number of requests they can make in a rolling 60 second window. Users transmitting requests that include their API key will see no change in service and may continue to make requests at the current rate.

Link:
https://nvd.nist.gov/general/news/API-Key-Announcement#:~:text=Requesting%20an%20NVD%20API%20key,address%20of%20a%20single%20requestor.

Users may obtain an API key by visiting https://nvd.nist.gov/developers/request-an-api-key

For additional information on both the CVE and CPE API, visit https://nvd.nist.gov/developers.