c# - How do I set return_uri for GoogleWebAuthorizationBroker.AuthorizeAsync?

Question

I am trying to use the Google Calendar API in my non-MVC .NET Web Application. (This appears to be an important distinction.)

I’ve tried to use code from this example at Google and this example at Daimto along with some helpful hints from a number of related posts here.

I have written the following method:

public void GetUserCredential( String userName )
{
    String clientId = ConfigurationManager.AppSettings[ "Google.ClientId" ];            //From Google Developer console https://console.developers.google.com
    String clientSecret = ConfigurationManager.AppSettings[ "Google.ClientSecret" ];    //From Google Developer console https://console.developers.google.com
    String[] scopes = new string[] {
            Google.Apis.Calendar.v3.CalendarService.Scope.Calendar          
    };

    // here is where we Request the user to give us access, or use the Refresh Token that was previously stored in %AppData%
    UserCredential credential = GoogleWebAuthorizationBroker.AuthorizeAsync( new ClientSecrets
    {
        ClientId = clientId,
        ClientSecret = clientSecret             
    }, scopes, userName, CancellationToken.None, new FileDataStore( "c:\temp" ) ).Result;

    // TODO: Replace FileDataStore with DatabaseDataStore
}

Problem is, when Google’s OAuth2 page is called, redirect_uri keeps getting set to http://localhost:<some-random-port>/authorize. I have no idea how to set this to something else, as in the following example URL generated by AuthorizeAsync:

https://accounts.google.com/o/oauth2/auth?access_type=offline
    &response_type=code
    &client_id=********.apps.googleusercontent.com
    &redirect_uri=http:%2F%2Flocalhost:40839%2Fauthorize%2F
    &scope=https:%2F%2Fwww.googleapis.com%2Fauth%2Fcalendar

Google responds with a redirect_uri_mismatch error page with the message:

“The redirect URI in the request: http://localhost:XXXXX/authorize/ did not match a registered redirect URI”

I can only register so many Redirect URI’s in my Google Developer’s Console Credentials page. I’m not inclined to register 65535 ports, and I want to use a page other than /authorize on my site. Specifically, I want to use, during development, http://localhost:888/Pages/GoogleApiRedirect but have no clue as to where I would set this, beyond what I've done in the Developer’s Console.

How do I explicitly set the value of redirect_uri? I am also open to a response in the form “This approach is completely wrong.”

EDIT:

After playing with this over the past day, I've discovered that by using the Client ID/Client Secret for the Native Application rather than the Web Application, I can at least get to Google's web authorization page without it complaining about a redirect_uri_mismatch. This is still unacceptable, because it still returns to http://localhost:<some-random-port>/authorize, which is outside the control of my web application.

Answer 1

You can use this code: (original idea from http://coderissues.com/questions/27512300/how-to-append-login-hint-usergmail-com-to-googlewebauthorizationbroker)

dsAuthorizationBroker.RedirectUri = "my localhost redirect uri";
UserCredential credential = await dsAuthorizationBroker.AuthorizeAsync(...

dsAuthorizationBroker.cs

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Auth.OAuth2.Requests;
using Google.Apis.Util.Store;

namespace OAuth2
{    
    public class dsAuthorizationBroker : GoogleWebAuthorizationBroker
    {
        public static string RedirectUri;

        public new static async Task<UserCredential> AuthorizeAsync(
            ClientSecrets clientSecrets,
            IEnumerable<string> scopes,
            string user,
            CancellationToken taskCancellationToken,
            IDataStore dataStore = null)
        {
            var initializer = new GoogleAuthorizationCodeFlow.Initializer
            {
                ClientSecrets = clientSecrets,
            };
            return await AuthorizeAsyncCore(initializer, scopes, user,
                taskCancellationToken, dataStore).ConfigureAwait(false);
        }

        private static async Task<UserCredential> AuthorizeAsyncCore(
            GoogleAuthorizationCodeFlow.Initializer initializer,
            IEnumerable<string> scopes,
            string user,
            CancellationToken taskCancellationToken,
            IDataStore dataStore)
        {
            initializer.Scopes = scopes;
            initializer.DataStore = dataStore ?? new FileDataStore(Folder);
            var flow = new dsAuthorizationCodeFlow(initializer);
            return await new AuthorizationCodeInstalledApp(flow, 
                new LocalServerCodeReceiver())
                .AuthorizeAsync(user, taskCancellationToken).ConfigureAwait(false);
        }
    }


    public class dsAuthorizationCodeFlow : GoogleAuthorizationCodeFlow
    {
        public dsAuthorizationCodeFlow(Initializer initializer)
            : base(initializer) { }

        public override AuthorizationCodeRequestUrl
                       CreateAuthorizationCodeRequest(string redirectUri)
        {
            return base.CreateAuthorizationCodeRequest(dsAuthorizationBroker.RedirectUri);
        }
    }    
}