AWS CDK IAM Typescript: iterating over an array of custom policies to assign

Question

I'm trying to map over a list of policies when creating IAM users in CDK (Typescript). The list looks like this:

name: "group",
    managedPolicies: [
      "IAMUserChangePassword",
      "job-function/SystemAdministrator",
    ],
    customPolicies: [
      "ManageMFACustomPolicy",
    ],

then the groups are added by

 props.groups.forEach((group) => {
  const iamGroup = new iam.Group(scope, group.name, {
    groupName: group.name,
    managedPolicies: group.managedPolicies?.map(iam.ManagedPolicy.fromAwsManagedPolicyName),
    customPolicies: group.customPolicies?.map(iam.fromManagedPolicyName.managedPolicyName),
  });

My issue is that custom policies are treated differently than managed policies. The managed policies mapping works. The custom policy does not. I know that the policy itself works if I explicitly assign it.

This is the error I get

Argument of type '{ groupName: string; managedPolicies: iam.IManagedPolicy[]; customPolicies: unknown[]; }' is not assignable to parameter of type 'GroupProps'.
  Object literal may only specify known properties, and 'customPolicies' does not exist in type 'GroupProps'.

  customPolicies: group.customPolicies?.map(iam.fromManagedPolicyName.managedPolicyName),

I realize now from the group construct docs that I was trying to use a nonexistent prop. Is there another method I should try to enumerate and add the array of custom policies? I'm just getting started with the CDK so I'm probably missing it in the docs. TIA!

UPDATE ----

I just wanted to update this, my idea about switching the type to managedpolicy doesn't work because they have to be ref'd via ARN so you get

Policy arn:aws:iam::aws:policy/ManageMFA does not exist or is not attachable. (Service: AmazonIdentityManagement; Status Code: 404; Error Code: NoSuchEntity; R equest ID: fc8ae611-74bc-4e46-8f94-f2d3b5dff0cc; Proxy: null) 

Jason's answer about inlinepolicy is correct

Answer 1

There isn't a customPolicies attribute on IAM Group Props . Are you just trying to attach a named inline policy? For that you'd need to create the group and then call attachInlinePolicy . That call requires a full policy though, not just a name.

If you are just trying to attach a named policy that you created (aka Customer Managed Policy) it would be the same as an AWS managed policy, so it goes in the same list as the others.