Cloudformation: substitute variable in map key - aws-cloudformation

Question

I have a role defined like this:
AWSTemplateFormatVersion: "2010-09-09"
Parameters:
AWSAccountId:
Type: String
OidcProvider:
Type: String
AppNamespace:
Type: String
AppServiceAccountName:
Type: String
Resources:
CloudWatchRole:
Type: "AWS::IAM::Role"
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
-
Effect: "Allow"
Principal:
Federated:
- !Join ["", [ "arn:aws:iam::", !Ref AWSAccountId, ":oidc-provider/", !Ref OidcProvider ] ]
Action:
- "sts:AssumeRoleWithWebIdentity"
Condition:
StringEquals:
!Sub ${OidcProvider}:sub: "system:serviceaccount:${AppNamespace}:${AppServiceAccountName}"
My challenge is how to substitute parameters in the StringEquals section. Everything works in the Federated block. But in the StringEquals block I couldn't get join or sub to work.
With the code as is, I get error message:
An error occurred (ValidationError) when calling the CreateStack operation:
Template format error[/Resources/CloudWatchRole/Properties/AssumeRolePolicyDocument/
Statement/0/Condition/StringEquals] map keys must be strings; received a map instead
So, I guess my issue is how to substitute variables in the keys of a map. UserData didn't help either.

Answer 1

You problem is on Federated not on StringEquals.
Federated value needs to be string but you define it as Map. Please remove - before !Join.
AWSTemplateFormatVersion: "2010-09-09"
Parameters:
AWSAccountId:
Type: String
OidcProvider:
Type: String
AppNamespace:
Type: String
AppServiceAccountName:
Type: String
Resources:
CloudWatchRole:
Type: "AWS::IAM::Role"
Properties:
AssumeRolePolicyDocument: !Sub
- |
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Federated": "${IamOidcProviderArn}"
},
"Action": "sts:AssumeRoleWithWebIdentity",
"Condition": {
"StringEquals": {
"${OidcProvider}:sub": "system:serviceaccount:${AppNamespace}:${AppServiceAccountName}"
}
}
}
]
}
- IamOidcProviderArn: !Join
- ''
- - 'arn:aws:iam::'
- !Ref AWSAccountId
- ':oidc-provider/'
- !Ref OidcProvider
OidcProvider: !Ref OidcProvider
AppNamespace: !Ref AppNamespace
AppServiceAccountName: !Ref AppServiceAccountName