`STSClientConfig` and `NodeHttpHandlerOptions` are different types, but all have optional properties only. That means that a call like this:

```ts
const credentials = await fromTemporaryCredentials({
  masterCredentials: mainCredentials.credentials,
  params: {
    RoleArn: roleArn,
    ExternalId: externalId,
    RoleSessionName: `aws-cdk-${safeUsername()}`,
    ...additionalOptions,
    TransitiveTagKeys: additionalOptions?.Tags ? additionalOptions.Tags.map((t) => t.Key!) : undefined,
  },
  clientConfig: {
    region,
    ...this.requestHandler, // type NodeHttpHandlerOptions
  },
})();
```

compiles just fine, when the intention was to write:

```ts
fromTemporaryCredentials({
  ...
  clientConfig: {
    region,
    requestHandler: this.requestHandler, // type NodeHttpHandlerOptions
  },
});
```

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