Ask HN: What's the Right Answer for API Authentication over HTTPS?

I've found a few good articles but they seem to disagree with regard to how many layers of security are required. Looking at other popular APIs doesn't offer much clarity. Twilio uses basic auth + HTTPS, Twitter uses OAUTH, AWS uses HMAC.. WTF?

Specifically if I'm using HTTPS, can I get by with a simple secret key sent with each request? I'm trying to balance ease of use with security. I don't want to require the API user to sign the payload/query using their private key if I can avoid it.