Google OAuth 2.0 authorization service implementation in .NET MAUI

Hello Programmers!, So today we'll learn that how to implement google OAuth 2.0 authorization service & integrate in .NET MAUI using WebView controls.

Step - 1 :

Create your Google Developer Account at Google Developer , if you han't any!
Open Cloud Console and click on DropDown menu then create on "New Project".

Step - 2 :

Go to "API & Services Tab by Clicking on menu icon of current project then Click on "Credentials".

Click on "Create Credentials" Button and select "Oauth client ID" option.

Step - 3 :

Select Application Type accroding to your requirement & provide Name.

Add redirect URI for app on which user is redirected after authorized.
Click on "Create Button"
Get the Client Id & Client Secrets.

STEP - 4 :

Setup basic maui App.
create authorization service & add below code.

namespace App
{
    public static class Auth
    {
        public static string ConstructGoogleSignInUrl()
        {
            // Specify the necessary parameters for the Google Sign-In URL
            const string clientId = "your_app_clientId";

            const string responseType = "code";
            const string accessType = "offline";
            const string redirect_uri = "your_app_redirect_uri";

            // Construct the Google Sign-In URL
            return "https://accounts.google.com/o/oauth2/v2/auth" +
                            $"?client_id={Uri.EscapeDataString(clientId)}" +
                            $"&redirect_uri={Uri.EscapeDataString(redirect_uri)}" +
                            $"&response_type={Uri.EscapeDataString(responseType)}" +
                            $"&scope={Uri.EscapeDataString(scope)}" +
                            $"&access_type={Uri.EscapeDataString(accessType)}" +
                            "&include_granted_scopes=true" +
                            "&prompt=consent";


        }


    }
}

Step - 5 :

Load webview with the google login screen on button click.

private void OnGetFilesClicked(object sender, EventArgs e)
    {
        WebView _signInWebView = new WebView
        {
            Source = Auth.ConstructGoogleSignInUrl(),
            VerticalOptions = LayoutOptions.Fill,
        };

    }
ContentPage signInContentPage = new ContentPage
        {
            Content = grid,
        };

        try
        {
            Application.Current.MainPage.Navigation.PushModalAsync(signInContentPage);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }

Step - 6 :

The Google Login screen is visible after clicked on button. Fill the user email id & password, Click "Allow" button on oauth consent scrren.

you will get the code in the redirect URL if user authorized successfully.

Step - 7 :

Get access token from the code which was provided by URL after authorizing a user.
- Add required nuget packages 1) Newtonsoft

 public static (string, string) ExchangeCodeForAccessToken(string code)
        {

            // Configure the necessary parameters for the token exchange
            const string clientId = "your_app_client_id";
            const string clientSecret = "your_app_client_secret";
            const string redirectUri = "your_app_redirect_URI";

            // Create an instance of HttpClient
            using (HttpClient client = new HttpClient())
            {
                // Construct the token exchange URL
                const string tokenUrl = "https://oauth2.googleapis.com/token";

                // Create a FormUrlEncodedContent object with the required parameters
                FormUrlEncodedContent content = new FormUrlEncodedContent(new Dictionary<string, string>
              {
                   { "code", code },
                   { "client_id", clientId },
                   { "client_secret", clientSecret },
                   { "redirect_uri", redirectUri },
                   { "grant_type", "authorization_code" }
              });

                // Send a POST request to the token endpoint to exchange the code for an access token
                HttpResponseMessage response = client.PostAsync(tokenUrl, content).Result;

                // Check if the request was successful
                if (response.IsSuccessStatusCode)
                {
                    // Read the response content
                    string responseContent = response.Content.ReadAsStringAsync().Result;

                    // Parse the JSON response to extract the access token
                    JObject json = JObject.Parse(responseContent);
                    string accessToken = json.GetValue("access_token").ToString();
                    string refreshToken = json.GetValue("refresh_token").ToString();
                    return (accessToken, refreshToken);
                }
                else
                {
                    // Exception:  "Token exchange request failed with status code: {response.StatusCode}"
                }
            }

            return (null, null);
        }

Get the access_token & refresh_token which is used to create credentials for access services API such as Drive , Gmail API etc.

// other code...

_signInWebView.Navigating += (sender, e) =>
       {

           string code = Auth.OnWebViewNavigating(e, signInContentPage);
           if (e.Url.StartsWith("http://localhost") && code != null)
           {

               (string access_token, string refresh_token) = Auth.ExchangeCodeForAccessToken(code);
           }

       };

You can find the necessary code in the repository mentioned below.

GithHub Repository

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Google OAuth 2.0 authorization service implementation in .NET MAUI

Jay Malli

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