Best practises for consuming multiple third party APIs in existing API

I'm trying to find out the best approach for designing the following scenarios.

Let's assume, that I already have, a REST API implementation, which is going to fetch books, from different providers and serve them back, to my own client.

1. Each provider offers a separate API for serving books to its consumers.
2. Each provider, has a completely different structure on the response from the previous one.
3. My client should always get exactly the same format, so the frontend-client application can handle the responses.

Some output examples:

Provider 1

[
  {
    "bookId": 32,
    "bookName": "foo",
    "author" : {
      "name" : "John",
      "surname": "Doe"
    },
    "publisher": {
      "name" : "Foo Books",
      "address": "New York"
    }
  },
  ...
]

Provider 2

[
  {
    "publisherCompany": {
      "name": "Foo Books",
      "position": "New York",
      "books": [
        {
          "id": 32,
          "title": "Foo",
          "author": {
            "name" : "John",
            "lastName": "Doe"
          } 
        },
        ...
      ]
    }
  },
 ...
]

Both of those 2 providers, are outputting the same values, but in different format. Moreover some keys are completely different.

What I'm looking for, is an Architectural Design or a Design Pattern, so i can map each different output, to my own format.

What i have tried in the past

• I had created my own Entities
• I had different services for each consumer and after fetching the data, i was instantiating my own entities and mapped the responses accordingly.
• After having my objects (Entities) filled with data, i was passing them to a transformer function to transform them to the desired output.

My questions:

• Is there any Design Pattern for this?
• Is there any terminology for this scenario so i can do a research?
• In which way you would approach this scenario?
• Any resources for reading ?

Thanks ;)