ASP.Net MVC5, Google OAuth 2.0 and Youtube API

I managed to do this using GooglePlus, haven't tried Google. Here's what I did:

Install the nugets:

> Install-Package Owin.Security.Providers
> Install-Package Google.Apis.Youtube.v3

Add this to Startup.auth.cs:

var g = new GooglePlusAuthenticationOptions();
g.ClientId = Constants.GoogleClientId;
g.ClientSecret = Constants.GoogleClientSecret;
g.RequestOfflineAccess = true;  // for refresh token
g.Provider = new GooglePlusAuthenticationProvider
{
    OnAuthenticated = context =>
    {
        context.Identity.AddClaim(new Claim(Constants.GoogleAccessToken, context.AccessToken));
        if (!String.IsNullOrEmpty(context.RefreshToken))
        {
            context.Identity.AddClaim(new Claim(Constants.GoogleRefreshToken, context.RefreshToken));
        }
        return Task.FromResult<object>(null);
    }
};

g.Scope.Add(Google.Apis.YouTube.v3.YouTubeService.Scope.YoutubeReadonly);
g.SignInAsAuthenticationType = DefaultAuthenticationTypes.ExternalCookie;
app.UseGooglePlusAuthentication(g);

The above code does two things:

1. Enable authentication via. Google+
2. Requests for the access token and the refresh token. The tokens are then added as a claim in the GooglePlus middleware.

Create a method that will store the claims containing the token to the database. I have this in the AccountController.cs file

private async Task StoreGooglePlusAuthToken(ApplicationUser user)
{
    var claimsIdentity = await AuthenticationManager.GetExternalIdentityAsync(DefaultAuthenticationTypes.ExternalCookie);
    if (claimsIdentity != null)
    {
        // Retrieve the existing claims for the user and add the google plus access token
        var currentClaims = await UserManager.GetClaimsAsync(user.Id);
        var ci = claimsIdentity.FindAll(Constants.GoogleAccessToken);
        if (ci != null && ci.Count() != 0)
        {
            var accessToken = ci.First();
            if (currentClaims.Count() <= 0)
            {
                await UserManager.AddClaimAsync(user.Id, accessToken);
            }
        }

        ci = claimsIdentity.FindAll(Constants.GoogleRefreshToken);
        if (ci != null && ci.Count() != 0)
        {
            var refreshToken = ci.First();
            if (currentClaims.Count() <= 1)
            {
                await UserManager.AddClaimAsync(user.Id, refreshToken);
            }
        }
    }

You'll need to call it in 2 places in the AccountController.cs: Once in ExternalLoginCallback:

case SignInStatus.Success:
var currentUser = await UserManager.FindAsync(loginInfo.Login);
if (currentUser != null)
{
    await StoreGooglePlusAuthToken(currentUser);
}
return RedirectToLocal(returnUrl);

and once in ExternalLoginConfirmation:

var user = new ApplicationUser { UserName = model.Email, Email = model.Email };
var result = await UserManager.CreateAsync(user);
if (result.Succeeded)
{
    result = await UserManager.AddLoginAsync(user.Id, info.Login);
    if (result.Succeeded)
    {
        await StoreGooglePlusAuthToken(user);
        await SignInManager.SignInAsync(user, isPersistent: false, rememberBrowser: false);
        return RedirectToLocal(returnUrl);
    }
}

Now that we've got the users access token and refresh token we can use this to authenticate the user.

I tried a simple search I saw in the examples and it worked:

private async Task<Models.YouTubeViewModel> Search(string searchTerm)
{
    var user = (ClaimsPrincipal)Thread.CurrentPrincipal;

    var at = user.Claims.FirstOrDefault(x => x.Type == Constants.GoogleAccessToken);
    var rt = user.Claims.FirstOrDefault(x => x.Type == Constants.GoogleRefreshToken);

    if (at == null || rt == null)
        throw new HttpUnhandledException("Access / Refresh Token missing");

    TokenResponse token = new TokenResponse
    {
        AccessToken = at.Value,
        RefreshToken = rt.Value
    };

    var cred = new UserCredential(new GoogleAuthorizationCodeFlow(
                new GoogleAuthorizationCodeFlow.Initializer()
                {
                    ClientSecrets = new ClientSecrets()
                                    {
                                        ClientId = Constants.GoogleClientId,
                                        ClientSecret = Constants.GoogleClientSecret
                                    }
                }
            ),
            User.Identity.GetApplicationUser().UserName,
            token
        );

    var youtubeService = new YouTubeService(new BaseClientService.Initializer()
    {
        ApplicationName = this.GetType().ToString(),
        HttpClientInitializer = cred,
    });

    var searchListRequest = youtubeService.Search.List("snippet");
    searchListRequest.Q = searchTerm;
    searchListRequest.MaxResults = 50;

    // Call the search.list method to retrieve results matching the specified query term.
    var searchListResponse = await searchListRequest.ExecuteAsync();

    Models.YouTubeViewModel vm = new Models.YouTubeViewModel(searchTerm);
    foreach (var searchResult in searchListResponse.Items)
    {
        switch (searchResult.Id.Kind)
        {
            case "youtube#video":
                vm.Videos.Add(new Models.Result(searchResult.Snippet.Title, searchResult.Id.VideoId));
                break;

            case "youtube#channel":
                vm.Channels.Add(new Models.Result(searchResult.Snippet.Title, searchResult.Id.ChannelId));
                break;

            case "youtube#playlist":
                vm.Playlists.Add(new Models.Result(searchResult.Snippet.Title, searchResult.Id.PlaylistId));
                break;
        }
    }

    return vm;
}

Model Classes

public class Result 
{
    public string Title { get; set; }
    public string Id { get; set; }

    public Result() { }

    public Result(string title, string id)
    {
        this.Title = title;
        this.Id = id;
    }
}

public class YouTubeViewModel
{
    public string SearchTerm { get; set; }

    public List<Result> Videos { get; set; }
    public List<Result> Playlists { get; set; }
    public List<Result> Channels { get; set; }

    public YouTubeViewModel()
    {
        Videos = new List<Result>();
        Playlists = new List<Result>();
        Channels = new List<Result>();
    }

    public YouTubeViewModel(string searchTerm)
        :this()
    {
        SearchTerm = searchTerm;
    }
}

Reference: http://blogs.msdn.com/b/webdev/archive/2013/10/16/get-more-information-from-social-providers-used-in-the-vs-2013-project-templates.aspx