Pagination Class

AuthenticationHelper.cs

public class AuthenticationHelper : IAuthenticationHelper
    {
        static string ApplicationName = "APPLICATIONNAME";
        static string RefreshToken = "YOURREFRESHTOKEN";

        public DriveService Authenticate()
        {
            var token = new TokenResponse
            {
                RefreshToken = RefreshToken
            };
            UserCredential credentials;
            using (var stream = File.OpenRead("credentials.json"))
            {
                credentials = new UserCredential(new GoogleAuthorizationCodeFlow(
                    new GoogleAuthorizationCodeFlow.Initializer()
                    {
                        ClientSecretsStream = stream,
                        Scopes = new List<string>()
                        {
                            DriveService.Scope.Drive
                        }
                    }), Environment.UserName, token);
            }

            // Create Drive API service.
            var service = new DriveService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credentials,
                ApplicationName = ApplicationName,
            });
            return service;
        }
    }

FileHandler.cs

public class FileHandler
    {
        private readonly DriveService _driveService;
        public FileHandler(DriveService driveService)
        {
            _driveService = driveService;
        }
        public IEnumerable<File> FetchFiles(string mimeType, int pageSize = 20)
        {
            FilesResource.ListRequest listRequest = _driveService.Files.List();

            listRequest.PageToken = Pagination.NextPageToken;
            listRequest.Q = mimeType;
            listRequest.PageSize = pageSize;
            listRequest.Fields = "nextPageToken, files(id, name, mimeType)";

            FileList execute = listRequest.Execute();
            Pagination.NextPageToken = execute.NextPageToken;
            IList<File> files = execute.Files;

            return files;
        }
    }

FilesController.cs

[Route("api/[controller]")]
    [ApiController]
    public class FilesController : ControllerBase
    {
        private readonly IAuthenticationHelper _authenticationHelper;
        public FilesController(IAuthenticationHelper authenticationHelper)
        {
            _authenticationHelper = authenticationHelper;
        }
        // GET api/files
        [HttpGet]
        public IEnumerable<File> Get()
        {
            var service = _authenticationHelper.Authenticate();
            var fileHandler = new FileHandler(service);
            var files = fileHandler.FetchFiles("mimeType='audio/mpeg'");
            return files;
        }
    }

IAuthenticationHelper.cs

public interface IAuthenticationHelper
    {
        DriveService Authenticate();
    }

Pagination.cs

public static class Pagination
    {
        public static string NextPageToken { get; set; }
    }

Startup.cs

services.AddTransient<IAuthenticationHelper, AuthenticationHelper>();