Possibility to use ApiKeyAuthentication NEST (.NET client) with Elasticsearch APP

Usecase: Enterpsie Elastic App Search 7.1.* is used for searchenigine as crawler.
We want to access data with from our .NET client NEST.
2 questions:
Can we use the ApiKeyAuthentication within NEST 7.1.15 package as client to access the data?
How can we check it for valid with Endpoint with "POSTMAN" what to fill in as field key (id or api_key)?