How a mobile app should authenticate to AWS

Question

I'm developing a mobile app that must access some AWS resources, so it needs authentication to AWS endpoint. The app doesn't manage users (sign-in, sign-out, register and so on).

My first solution was to create a IAM user dedicated to the mobile app and embed its credentials in the mobile app code. The app authenticate itself to AWS using the embedded credentials. It works, however AWS suggests to avoid embedding credentials directly in the app.

I think a better solution is Cognito. Because I don't need users management, I should use unauthenticated (guest) identity to request temporary AWS credentials.

However I don't understand why a guest Cognito identity is more secure than an embedded credentials. The mobile app receive a temporary AWS credentials by sending a Cognito Identity Pool ID, that is a long-term "number" embedded in the mobile app. If someone is able to find this Identity Pool ID, she can receive AWS credentials and access AWS resources as my official mobile app. It seems there's no difference between embedded AWS long-term credentials and huest Cognito access.

Why Cognito solution is better than embedded AWS credentials?

Answer 1

If you are creating unauthenticated access using identity pool, you are allowing public to access your AWS resources. Make sure you write your policy carefully and it won't matter if you use a single IAM user or cognito unauthenticated access as far as security is concerned.

Using federated identity will provide you benefits like getting statistics on usage and adding triggers to events. Also keep in mind that creating a single IAM user and then allowing multiple people to use these credentials is a "hack" way of doing what cognito federated unauthenticated idenity was designed to do. You might run into unexpected complications later if AWS decides to throttle this behavior of IAM.