If you're already in the AWS ecosystem or have worked in it, it's no problem. If you're used to "make OpenAI account, add credit card, copy/paste API key" it can be a bit daunting.
AWS does not use the exact same authn/authz/identity model or terminology as other providers, and for people familiar with other models, it's pretty non-trivial to adapt to. I recently posted a rant about this to https://www.reddit.com/r/aws/comments/1geczoz/the_aws_iam_id...
Personally I am more familiar with directly using API keys or auth tokens than AWS's IAM users (which are more similar to what I'd call "service accounts").
If you're looking for a generative AI model API only, I think Nova is not for you. If you want to build that capability into your cloud application, it uses exactly the model you expect and have, and you just add a new policy/role/whatever for whatever piece of it's going to use Nova.