C#' Dropbox login class (not platform specific)

DropboxManager.cs

using Dropbox.Api;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Babbacombe.MobileDmx {
    class DropboxManager : IDisposable {

        public string AppName { get; }
        public string AppKey { get; }
        public string RedirectUri { get; set; } = "https://localhost/authorize";

        public string AccessToken { get; private set; }

        public DropboxClient Client { get; private set; }

        public Func<Uri, string, Task<string>> LoginAsync { get; set; }

        public Func<Uri, string, string> Login { get; set; }

        public DropboxManager(string appName, string appKey, string savedAccessToken) {
            AppName = appName;
            AppKey = appKey;
            AccessToken = savedAccessToken;
        }

        public async Task<bool> SetupClientAsync() {
            if (Client != null) return true;
            if (!await obtainAccessToken()) return false;

            // Specify socket level timeout which decides maximum waiting time when on bytes are
            // received by the socket.
            var httpClient = new HttpClient(new WebRequestHandler { ReadWriteTimeout = 10 * 1000 }) {
                // Specify request level timeout which decides maximum time that can be spent on
                // download/upload files.
                Timeout = TimeSpan.FromMinutes(20)
            };

            var config = new DropboxClientConfig(AppName) {
                HttpClient = httpClient
            };

            Client = new DropboxClient(AccessToken, config);
            return true;
        }

        private async Task<bool> obtainAccessToken() {
            if (!string.IsNullOrWhiteSpace(AccessToken)) return true;

            var oAuth2State = Guid.NewGuid().ToString("N");
            var authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri(OAuthResponseType.Token, AppKey, new Uri(RedirectUri), oAuth2State);
            if (LoginAsync != null) {
                AccessToken = await LoginAsync(authorizeUri, oAuth2State);
            } else if (Login != null) {
                AccessToken = Login(authorizeUri, oAuth2State);
            }

            return !string.IsNullOrWhiteSpace(AccessToken);
        }

        /// <summary>
        /// To be called in the BrowserNavigating event of the browser.
        /// </summary>
        /// <param name="uri">The uri navigating to</param>
        /// <param name="oAuth2State">The oAuthState passed in the event args</param>
        /// <param name="accessToken">the AccessToken obtained</param>
        /// <returns>True to exit the browser, False to do nothing</returns>
        public virtual bool OnBrowserNavigating(Uri uri, string oAuth2State, out string accessToken) {
            accessToken = null;
            if (!uri.ToString().StartsWith(RedirectUri, StringComparison.OrdinalIgnoreCase)) {
                // we need to ignore all navigation that isn't to the redirect uri.
                return false;
            }
            try {
                OAuth2Response result = DropboxOAuth2Helper.ParseTokenFragment(uri);
                if (oAuth2State != result.State) return true;
                accessToken = result.AccessToken;
            } catch (ArgumentException) {
                // There was an error in the URI passed to ParseTokenFragment
            }
            return true;
        }

        #region IDisposable Support
        private bool disposedValue = false; // To detect redundant calls

        protected virtual void Dispose(bool disposing) {
            if (!disposedValue) {
                if (disposing) {
                    if (Client != null) {
                        Client.Dispose();
                        Client = null;
                    }
                }
                disposedValue = true;
            }
        }

        public void Dispose() {
            Dispose(true);
        }
        #endregion
    }
}