How to restricted to access AWS API Gateway endpoint by Cognito user id

Question

I am trying to implement an e-commerce application backend by using AWS Cognito, Api-Gateway, and Lambda.

To create a new Item, users must be logged in. Once created the item, the Logged used will be the creator of the item. I already created an Item-create endpoint and added the Cognito-JWT authorizer for the Apigateway endpoint.

Now I need to implement Item-update endpoint. The relevant Item update must be allowed only for the creator of the Item. API maybe like this.

/items/{item-id} PUT
body : { title, price... }
header { Authorization: Cognito-JWT-Token }

What is the best way to implement this kind of feature using the AWS ecosystem. Or any best practices to implement this kind of feature.

Answer 1

You would create a property owner for each item that is a user ID. Normally you'd use the sub claim from the token which is a unique ID. However, for various reasons, I wouldn't recommend using the subject value with cognito. You can use email just ensure safeguards are in place if someone deletes their account and a new one is created with the same email.

Whatever you choose, in your handler compare the owner with the validated token claim. Allow if they match, disallow if they don't.