Unable to use Xamarin.Forms WebView for Dropbox authentication - ios

Question

I've run into a problem using WebView to access the authorization uri necessary to authorize access by my Xamarin forms (running under iOS) app. I don't believe the problem lies with the WebView and the particular url, and not the Dropbox API itself.
First, I should mention that I am able to use WebView to access arbitrary web sites, so I know I am able to access the web generally from within my app.
In the code below you will see that I have two buttons set up. The first uses a WebView to successfully access the Wikipedia page for Xamarin. The second attempts to contact Dropbox in order to begin the authentication process. However, that request fails with the message:
Error (400) It seems the app you were using submitted a bad request. If you would like to report this error to the app's developer, include the information below. Invalid redirect_uri. Must be an absolute uri.
Initially, I thought that the problem was that the redirection uri wasn't registered correctly, but if I copy the url being passed to the webview (included below as a comment), and paste it directly into safari, the authentication page opens as expected. It is only when using WebView that I receive the error message. That makes me think that it's not the redirect_uri, or the url itself, but something in the way that the WebView is presenting it to dropbox.com.
Can anyone help me out? I've also tried taking a uri that works in Safari / Chrome and passing it directly to the webview (bypassing DropboxOAuth2Helper) without any luck. The uri will work in Safari, but not in the WebView.
public App()
{
Button xamarinBtn = new Button();
xamarinBtn.Text = "Xamarin";
xamarinBtn.Clicked += OnButtonClicked;
xamarinBtn.StyleId = "Xamarin";
Button dropboxBtn = new Button();
dropboxBtn.Text = "Dropbox";
dropboxBtn.Clicked += OnButtonClicked;
dropboxBtn.StyleId = "Dropbox";
StackLayout layout = new StackLayout();
layout.Children.Add(xamarinBtn);
layout.Children.Add(dropboxBtn);
ContentPage page = new ContentPage();
page.Content = layout;
MainPage = new NavigationPage(page);
}
private void OnButtonClicked(object sender, EventArgs e)
{
Button btn = sender as Button;
UrlWebViewSource source = new UrlWebViewSource();
if (btn.StyleId == "Xamarin")
{
source.Url = "https://en.wikipedia.org/wiki/Xamarin";
}
else if (btn.StyleId == "Dropbox")
{
string oauth2State = Guid.NewGuid().ToString("N");
Uri authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri(OAuthResponseType.Token, "d1612up7la63slo", "http://127.0.0.1:52475/authorize", oauth2State);
source.Url = authorizeUri.AbsoluteUri; // https://www.dropbox.com/oauth2/authorize?response_type=token&client_id=d1612up7la63slo&redirect_uri=http%3A%2F%2F127.0.0.1%3A52475%2Fauthorize&state=1062a614aa3d4e2e85cd84de32903987
}
WebView webView = new WebView();
webView.Source = source;
ContentPage page = new ContentPage();
page.Content = webView;
MainPage.Navigation.PushAsync(page);
}

Answer 1

You should add that as a OAuth 2 redirect URI for your app via the App Console:
After doing this, I tried OC code it works properly and can show the authorize view. But Unfortunately, the Dropbox for Xamarin failed. You can try to use another api to show this view:
Uri authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri("d1612up7la63slo");
source.Url = source.Url = authorizeUri.AbsoluteUri;