Thursday, September 26, 2013

ArcGIS Online Authentication with OAuth2 and Windows Store

image

User authentication is an important part of application design and development.  Authentication allows developers protect user privacy, store settings and access profile information such as a profile picture and other assorted details.

ArcGIS Online (or AGOL) is Esri’s cloud based solution for creating and sharing maps, apps and geographic services.  AGOL supports OAuth2, an open standard for user authentication.  This blog posting contains a code snippet that can help you connect to AGOL using OAuth2 authentication.  Please keep in mind that this functionality will become a core capability of the next release of Esri’s ArcGIS Runtime SDK for Windows Store apps.

In this example, when the user clicks the blue start button (see screenshot above) the following dialog appears.  If the user enters a valid username and password, the login dialog is dismissed and the app will navigate from the welcome page to the main application page.

image

Additional References:

 

public sealed partial class WelcomePage : LayoutAwarePage {
    private const string AGOL_OAUTH = "https://www.arcgis.com/sharing/oauth2/authorize";
    private const string AGOL_APPID = "<your app id>";
    private const string AGOL_REDIR = "http://maps.esri.com";
    private const string AGOL_GETTK = "https://www.arcgis.com/sharing/oauth2/token";
    //
    // CONSTRUCTOR
    //
    public WelcomePage() {
        this.InitializeComponent();

        // Button events
        this.ButtonLogin.Click += async (s, e) => {
            this.ButtonLogin.IsEnabled = false;
            await this.LogPortal();
            this.ButtonLogin.IsEnabled = true;
        };
    }
    private async Task LogPortal() {
        // Construct AGOL login url
        string query = string.Empty;
        query += string.Format("client_id={0}", AGOL_APPID);
        query += string.Format("&response_type={0}", "code");
        query += string.Format("&redirect_uri={0}", Uri.EscapeDataString(AGOL_REDIR));

        // Build url
        UriBuilder b = new UriBuilder(WelcomePage.AGOL_OAUTH) {
            Query = query
        };

        // Display 0Auth2 dialog
        WebAuthenticationResult w = await WebAuthenticationBroker.AuthenticateAsync(
            WebAuthenticationOptions.None,
            b.Uri,
            new Uri(AGOL_REDIR)
        );
        switch (w.ResponseStatus) {
            case WebAuthenticationStatus.Success:
                // Response ok?
                if (w.ResponseData == null) { return; }

                // Parse return uri
                Uri call = null;
                if (!Uri.TryCreate(w.ResponseData, UriKind.RelativeOrAbsolute, out call)) { return; }

                // Extract code
                string[] parameters = call.Query.TrimStart('?').Split('&');
                Dictionary<string, string> dict = new Dictionary<string, string>();
                foreach (string parameter in parameters) {
                    string[] parts = parameter.Split('=');
                    if (parts.Length != 2) { continue; }
                    dict.Add(parts[0], parts[1]);
                }
                var item = dict.FirstOrDefault(kvp => kvp.Key == "code");
                string code = item.Value;
                if (string.IsNullOrWhiteSpace(code)) { return; }

                // Build token request query
                string query2 = string.Empty;
                query2 += string.Format("client_id={0}", AGOL_APPID);
                query2 += string.Format("&grant_type={0}", "authorization_code");
                query2 += string.Format("&code={0}", code);
                query2 += string.Format("&redirect_uri={0}", Uri.EscapeDataString(AGOL_REDIR));

                // Build token request url
                UriBuilder builder = new UriBuilder(WelcomePage.AGOL_GETTK) {
                    Query = query2
                };

                // Get response
                HttpClient c = new HttpClient();
                string text = await c.GetStringAsync(builder.Uri);
                if (string.IsNullOrWhiteSpace(text)) { return; }

                // Parse json - extract token
                JsonValue jv = null;
                if (!JsonValue.TryParse(text, out jv)) { return; }
                JsonObject jo = jv.GetObject();
                string access = jo.GetNamedString("access_token");
                double expire = jo.GetNamedNumber("expires_in");
                string refresh = jo.GetNamedString("refresh_token");
                string username = jo.GetNamedString("username");

                // Instantiate portal
                ArcGISPortal portal = await ArcGISPortal.CreateAsync(null, null, access);

                // Store reference to portal
                QuizDataSource.Default.Portal = portal;

                // Navigate to main page
                this.Frame.Navigate(typeof(MainPage));

                break;
            case WebAuthenticationStatus.ErrorHttp:
                string http_errorcode = w.ResponseErrorDetail.ToString();
                this.GridWelcome.Visibility = Visibility.Visible;
                this.ErrorControl.Show(http_errorcode);
                break;
            case WebAuthenticationStatus.UserCancel:
            default:
                break;
        }
    }
}

Base93 - Integer Shortening in C#

base93

This post will describe a technique of shortening an integer by approximately 50%.  For example, the approximate coordinate extent of continental United States in web Mercator can be expressed in the following JSON representation.
{"xmin":-15438951,"ymin":1852835,"xmax":-5420194,"ymax":7485635},

…or simplified to:
-15438951,1852835,-5420194,7485635

…or shortened to:
-ji5l,2sk},cGyR,70o#

The principle being employed here is that numbers are normally expressed using the decimal or base ten numerical system.  This system requires ten characters (or “digits”), 0 to 9, to formulate a number.  However, because ASCII has 95 printable characters we can encode numbers using base 93 which can result in printed strings that are 50% shorter than their decimal cousins.  For example:

-15438951 to –ji5l, or
1852835 to 2sk}

Why not use all 128 ASCII characters?  Well. 33 are non-printable and the characters “,” and “-“ are reserved for delimiter and negation respectively.

Lastly, to reduce the overall length of extents, the xmax is expressed as a width and ymax as a height.  At small scales the benefit of this technique is negligible (if any) but significant at large scales.

Please see below for source code and test method.

using System;
using System.Diagnostics;
using System.Globalization;
using System.Linq;

namespace ESRI.PrototypeLab.Base93 {
    public static class Base93Extension {
        private const string CHRS =
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" +
" !?\"'`^#$%@&*+=/.:;|\\_<>[]{}()~"; public static string ToShortenedString(this int num) { string result = string.Empty; if (num < 0) { result += "-"; num = Math.Abs(num); } int len = CHRS.Length; int index = 0; while (num >= Math.Pow(len, index)) { index++; } index--; while (index >= 0) { int pow = (int)Math.Pow(len, index); int div = num / pow; result += CHRS[div]; num -= pow * div; index--; } return result; } public static int ToUncompressedInteger(this string s) { int result = 0; int len = CHRS.Length; int index = 0; var chars = s.ToCharArray(); foreach (char c in chars.Reverse().Where(x => x != '-')) { int pow = (int)Math.Pow(len, index); int ind = CHRS.IndexOf(c); result += pow * ind; index++; } if (chars.First() == '-') { result *= -1; } return result; } internal static void Test() { int max = int.MaxValue; string com = max.ToShortenedString(); int unc = com.ToUncompressedInteger(); double x = (double)com.Length /
(double)max.ToString(CultureInfo.InvariantCulture).Length; Debug.WriteLine("Max Integer: {0}", max); Debug.WriteLine("Compressed: {0}", com); Debug.WriteLine("Uncompressed: {0}", unc); Debug.WriteLine("Compression: {0:P}", 1 - x); } } }