Control role permission in AWS - amazon-web-services

Question

I'm new to AWS. I'm developing an application using Spring boot. I use AWS cognito for the sign in and sign up. I created a group called ROLE_ADMIN in cognito and connect with IAM role which was also created by me as ROLE_ADMIN_IAM.
I'm using AWS Api gateway (HTTP Apis, but similarly REST Apis) to communicate with Apis. Then integrated the Cognito jwt authorizer in Api gateway.
Everything working perfectly. The problem I'm facing now is, when a user sign in, I need to prevent few Apis based on his role which is in cognito groups. So I tried to attach policies to IAM role (ROLE_ADMIN_IAM already created), but it doesn't work.
This is what I attached to ROLE_ADMIN_IAM
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Deny",
"Action": [
"apigateway:GET"
],
"Resource": [
"arn:aws:apigateway:ap-south-1::/apis/09bccr0"
]
}
]
}
I tried restrict every resources also. But doesn't work
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Deny",
"Action": "*",
"Resource": "*"
}
]
}
I'm afraid whether the way I tried is wrong or correct? I've been working for days. But couldn't find any solution. Please anyone give me a solution. Thanks in advance.
Update 1.
Since this doesn't work, I created a Identity pool and attached user pool Id and client id with it. It automatically creates two Roles for authentication user and unauthentication user. Then I went to Api gateway and changed the authorizer to IAM. The documentation itself says when we use IAM as an authorizer we need to use Signature 4 version. (I switched to IAM form cognito jwt, because I don't find any documentation or article say I can go with cognito jwt when we use Identity pool to define roles).
In the react application, I use amplify. When I configure Identity pool, it provides temporary Accesskey and SecretKey after a successful login. I tried to use it with postman -> Authorization -> AWS Signature, it always gives {"message":"Forbidden"}

Answer 1

When you create a group in a Cognito user pool you need to attach proper IAM role to that group. IAM policy that allows actual API calls should look like that:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"execute-api:Invoke"
],
"Resource": [
"arn:aws:execute-api:us-east-1:*:a123456789/test/POST/mydemoresource/*"
]
}
]
}
You just need to replace demo string with your API Gateway ARN, method and endpoint. Pay attention to the "execute-api:Invoke" action.
Permission "apigateway:GET" does not allow you to call an API but to get service information about API. "apigateway:*" permissions allow you to make management AWS API call not actual API call.
For more information please check these articles:
Management calls
Execution calls