AWS Appsync + HTTP DataSources + AWS IAM - aws-api-gateway

Question

I'm deploying some REST apis using API Gateway and Lambda Functions. Because of some architectural restrictions, the API must be available only by REST endpoints. On top of the API's I need to implement a GraphQL interface to allow part of our users to query this data. To deploy the GraphQL endpoints I'm using AWS AppSync. Based on that restrictions, I created the AppSync HTTP DataSource pointing to API Gateway stage url (https://api-gateway-api-id.execute-api.eu-central-1.amazonaws.com). It worked fine. Then I secured the API Gateway REST endpoint to use AWS_IAM, created a role for the datasource with permissions to invoke-api on the selected api inovocation arn and configured the HTTP Datasource using aws cli.
For example, here is my Role:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "",
"Effect": "Allow",
"Principal": {
"Service": "appsync.amazonaws.com"
},
"Action": "sts:AssumeRole"
}
]
}
And here is the policy attached to this role:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "VisualEditor0",
"Effect": "Allow",
"Action": "execute-api:Invoke",
"Resource": "arn:aws:execute-api:eu-central-1:9999999999:api-gateway-api-id/*/*/*"
}
]
}
And after all of that I updated my data source from aws cli with the following config:
{
"dataSource": {
"dataSourceArn": "arn:aws:appsync:eu-central-1:99999999999:apis/appsync-pi-id/datasources/Echo",
"name": "Echo",
"type": "HTTP",
"serviceRoleArn": "arn:aws:iam::99999999999:role/roleName",
"httpConfig": {
"endpoint": "https://api-gateway-api-id.execute-api.eu-central-1.amazonaws.com",
"authorizationConfig": {
"authorizationType": "AWS_IAM",
"awsIamConfig": {
"signingRegion": "eu-central-1",
"signingServiceName": "appsync"
}
}
}
}
}
Now when I try to make a query, I get the following error:
Credential should be scoped to correct service: 'execute-api'
As I understand, the correct service to be used to formulate the signature is the execute-api. I have some experience creating AWSV4 Signatures and knows that for this case it would be this one.
Somebody knows where I'm making a mistake?

Answer 1

With help from Ionut Trestian I found the error. I changed the configuration to use a different signatureService, like the following:
{
"dataSource": {
"dataSourceArn": "arn:aws:appsync:eu-central-1:99999999999:apis/appsync-pi-id/datasources/Echo",
"name": "Echo",
"type": "HTTP",
"serviceRoleArn": "arn:aws:iam::99999999999:role/roleName",
"httpConfig": {
"endpoint": "https://api-gateway-api-id.execute-api.eu-central-1.amazonaws.com",
"authorizationConfig": {
"authorizationType": "AWS_IAM",
"awsIamConfig": {
"signingRegion": "eu-central-1",
"signingServiceName": "execute-api"
}
}
}
}
}
Apparently I didn't understand correctly the configuration values. In my defense, I didn't found any documentation regarding this options, only a few examples scattered through the web. :-)

Answer 2

In case anyone else ends up here as I did wondering what else can be placed as a signingServiceName (I was looking for s3 specifically), I found this helpful blog post https://blog.iamjkahn.com/2019/12/invoking-even-more-aws-services-directly-from-aws-appsync.html