Berlin(DE) City Open Data.
City, Berlin API is a free Government API that requires no API key, is served over HTTPS and has unconfirmed CORS support.

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.
Yes. The City, Berlin API is listed in the Government 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.
No. The City, Berlin API requires no authentication, so you can start making requests without signing up.
CORS support for the City, Berlin API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The City, Berlin API is served over HTTPS, so it's safe to use in production.