US government job board.
USAJOBS API is a free Jobs API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from developer.usajobs.gov.

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The USAJOBS API is provided by USAJOBS (developer.usajobs.gov).
Yes. The USAJOBS API is listed in the Jobs 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 USAJOBS API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the USAJOBS API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The USAJOBS API is served over HTTPS, so it's safe to use in production.