AWS AssumeRole in Typescript using aws-sdk

Question

I am trying to assume a role in my typescript application. I have a User set up in AWS and defined as my default user on my machine. I have a Role defined in IAM with the permissions I want to have and the associated Trust Policy to allow my local user to assume it (as far as I can tell). Here is the Trust Policy for the Role (Note I am using 0123456789 as a substitute for my actual Account Id):

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::0123456789:user/LocalUser"
            },
            "Action": "sts:AssumeRole",
            "Condition": {}
        }
    ]
}

Here are the Permissions of the Role

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowIAM",
            "Effect": "Allow",
            "Action": [
                "iam:*",
            ],
            "Resource": "*"
        }
    ]
}

The User also has the following in it's Permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AsssumeRole",
            "Effect": "Allow",
            "Action": [
                "sts:AssumeRole"
            ],
            "Resource": [
                "arn:aws:iam::0123456789:role/TestRole"
            ]
        }
    ]
}

Finally here is an MWE of my index.ts file:

import {STSClient,AssumeRoleCommand,GetCallerIdentityCommand} from "@aws-sdk/client-sts";
import { IAMClient, GetRoleCommand } from "@aws-sdk/client-iam";

const getCredentials = async (accountId: string, roleName: string) => {
  const sts_client = new STSClient({ region: "us-east-1" });

  const command = new AssumeRoleCommand({
    RoleArn: `arn:aws:iam::${accountId}:role/${roleName}`,
    RoleSessionName: "TestSession",
  });
  const response = await sts_client.send(command);
  const creds = response.Credentials;

  console.log(creds); // Returns AccessKeyId, SecretAccessKey, SessionToken and Expiration
  return {
    accessKeyId: creds?.AccessKeyId,
    secretAccessKey: creds?.SecretAccessKey,
    sessionToken: creds?.SessionToken,
    region: "us-east-1",
  };
};

export default async function run() {
  const RoleName = "TestRole";
  const AccountId = "0123456789";

  const accessCreds = await getCredentials(AccountId, RoleName);

  const sts_client_tester = new STSClient(accessCreds);
  const sts_identity = await sts_client_tester.send(
    new GetCallerIdentityCommand({})
  );
  console.log(sts_identity); // Returns Local Account, not Assumed Account!!

  const iam_client = new IAMClient(accessCreds);
  const iam_input = { RoleName: RoleName };
  const iam_command = new GetRoleCommand(iam_input);
  const iam_response = await iam_client.send(iam_command);
  console.log(iam_response); // Permission Error because Local Account does not have permissions
}

Note that the AssumeRoleCommand does not throw any error when I send() it, and it is successful, but when I try to use these credentials, it is not working.