How do I validate properties with a custom schema?

[iainelder]

cfn-lint Version

cfn-lint 0.78.1

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I want to use aws-sso-util and cfn-lint together. aws-sso-util provides a macro which fakes a custom type called SSOUtil::SSO::AssignmentGroup.

My template looks like this:

AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS-SSO-Util-2020-11-08

Parameters:
  InstanceArn:
    Type: String
    Default: arn:aws:sso:::instance/ssoins-ffffffffffffffff

Resources:
  ReadOnly:
    Type: AWS::SSO::PermissionSet
    Properties:
      Name: ReadOnly
      InstanceArn: !Ref InstanceArn
      ManagedPolicies:
        - arn:aws:iam::aws:policy/ReadOnlyAccess

  AssignmentGroup:
    Type: SSOUtil::SSO::AssignmentGroup
    Properties:
      Name: ReadOnly
      InstanceArn: !Ref InstanceArn
      Principal:
        - Type: USER
          Id: ffffffff-ffff-ffff-ffff-ffffffffffffffff
      PermissionSet:
        - !GetAtt ReadOnly.PermissionSetArn
      Target:
        - Type: AWS_OU
          Id: ou-zzzz-zzzzzzzz

By default cfn-lint of course fails to recognize the custom type.

$ cfn-lint --template Macro-Test.yaml --region eu-central-1
E3001 Invalid or unsupported Type SSOUtil::SSO::AssignmentGroup for resource AssignmentGroup in eu-central-1
Macro-Test.yaml:19:5

I think I'm supposed to use --registry-schemas to solve this, but I've had limited success because of the missing documentation.

#2321 says that to lint Datadog::Monitors::Monitor you need to pass a directory of third-party resource schemas and points to #1732 for a partial solution.

SSOUtil::SSO::AssignmentGroup is not a real registered type, but is faked by macro preprocessing, so there is no schema to download. As far as I know, no one ever wrote that schema.

I created a file called custom-schema/AssignmentGroup.json with this content:

{
    "typeName": "SSOUtil::SSO::AssignmentGroup"
}

cfn-lint produces no output when I pass the the folder name, which I think means it now at least accepts the type name.

$ cfn-lint --template Macro-Test.yaml --region eu-central-1 --registry-schemas custom-schema/

I also want to validate the properties, and this is where I get lost.

I extend the custom schema to look like this:

{
    "typeName": "SSOUtil::SSO::AssignmentGroup",
    "properties": {
        "Color": {
            "Type": "String"
        }
    },
    "required": ["Color"]
}

My intention is to declare a required Color property. This should make cfn-lint fail again because my template doesn't have a Color property anywhere.

But cfn-lint still gives no output in this case.

There might be something wrong with the schema, but I'm unsure how to validate it.

What am I missing?