Public Transport consumer.
Transport for Sweden API is a free Transportation API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
Details from trafiklab.se.

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The Transport for Sweden API is provided by Trafiklab (trafiklab.se).
Yes. The Transport for Sweden API is listed in the Transportation 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 Transport for Sweden API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Transport for Sweden API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Transport for Sweden API is served over HTTPS, so it's safe to use in production.