{
          "version" : "2018-05-29",
          "operation" : "Query",
          "query" : {
              "expression": "userid = :userid",
              "expressionValues" : {
                  ":userid" : $util.dynamodb.toDynamoDBJson(${context.identity.sub})
              }
          },
          "index": "useridGSI"
        }