How should I format a post_filter query to match a string inside of a string?

[simonstiph (Simon S.)]

I have an array of articles (i.e. from newspapers) in a MongoDB database that is indexed into Elasticsearch. Each article has any number of authors, like: ['John Doe', 'Jane Doe'].

In Es, I have aggregation by author working properly, but I also want to apply a post_filter to filter results by author. How should a post_filter query be designed to handle this?

Article schema in Es (can be modified if necessary):

{
  ...
  authors: ['Michael Jordan', 'Kobe Bryant'],
  authorsString: 'Michael Jordan;Kobe Bryant;'
}

This is an example query before applying the post_filter:

{
  ...
  aggs: {
    authors: {
      terms: {
        field: 'authors.keyword',
      },
    },
  },
  post_filter: {},
}

If I want to find articles of which at least one of the authors is "Michael Jordan", how do I use post_filter to do so?