now.json

{
  "env": {
    "REACT_APP_FIREBASE_API_KEY": "@firebase-api-key",
    "REACT_APP_FIREBASE_AUTH_DOMAIN": "@firebase-auth-domain",
    "REACT_APP_FIREBASE_DATABASE_URL": "@firebase-database-url",
    "REACT_APP_FIREBASE_PROJECT_ID": "@firebase-project-id",
    "REACT_APP_FIREBASE_STORAGE_BUCKET": "@firebase-storage-bucket",
    "REACT_APP_FIREBASE_MESSAGING_SENDER_ID": "@firebase-messaging-sender-id",
    "REACT_APP_FIREBASE_APP_ID": "@firebase-app-id",
    "REACT_APP_FIREBASE_MEASUREMENT_ID": "@firebase-measurement-id",
    "API_KEY": "@api-key",
    "REACT_APP_DATA_ENDPOINT": "@data-endpoint"
  },
  "build": {
    "env": {
      "REACT_APP_FIREBASE_API_KEY": "@firebase-api-key",
      "REACT_APP_FIREBASE_AUTH_DOMAIN": "@firebase-auth-domain",
      "REACT_APP_FIREBASE_DATABASE_URL": "@firebase-database-url",
      "REACT_APP_FIREBASE_PROJECT_ID": "@firebase-project-id",
      "REACT_APP_FIREBASE_STORAGE_BUCKET": "@firebase-storage-bucket",
      "REACT_APP_FIREBASE_MESSAGING_SENDER_ID": "@firebase-messaging-sender-id",
      "REACT_APP_FIREBASE_APP_ID": "@firebase-app-id",
      "REACT_APP_FIREBASE_MEASUREMENT_ID": "@firebase-measurement-id",
      "API_KEY": "@api-key",
      "REACT_APP_DATA_ENDPOINT": "@data-endpoint"
    }
  }
}