
Passwords which have previously been exposed in data breaches.
HaveIBeenPwned API is a free Security API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from haveibeenpwned.com.

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The HaveIBeenPwned API is provided by Have I Been Pwned (haveibeenpwned.com).
Yes. The HaveIBeenPwned 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 HaveIBeenPwned API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the HaveIBeenPwned API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The HaveIBeenPwned API is served over HTTPS, so it's safe to use in production.