The industry’s first hacker API that helps increase productivity towards creative bug bounty hunting.
HackerOne API is a free Security API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from api.hackerone.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
A REST API to access high level cryptographic functions and methods
The HackerOne API is provided by HackerOne API (api.hackerone.com).
Yes. The HackerOne API is listed in the Security category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The HackerOne API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the HackerOne API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The HackerOne API is served over HTTPS, so it's safe to use in production.