Authentication is handled using basic access authentication.
You'll find the required username and password on the api page under settings.
Some methods (often prefix with 'public') are available for publishing purposes and do not need authentication.
Since we're using basic authentication it's easy to try it out in your browser. Click the link below and fill in your api credentials and have a look at the response (you should have at least one video inside your account to see anything useful).
https://www.streamio.com/api/v1/videos.json
You can also use basic authentication in curl through the -u or --user arguments.
curl -u username:password https://www.streamio.com/api/v1/videos curl --user username:password https://www.streamio.com/api/v1/videos
Another alternative is to put the username and password directly in the url.
curl https://username:password@streamio.com/api/v1/videos