Yammer external login setup with ASP.NET Core

Posted by Anuraj on Friday, May 25, 2018 Reading time :3 minutes

ASP.NET Core Yammer OAuth 2

This post shows you how to enable your users to sign in with their Yammer account. Similar to the other social networks, the authentication is an OAuth 2 flow, beginning with the user authenticating with their Yammer credentials. The user then authorizes your app to connect to their Yammer network. The end result is a token that your app will use to write events to Yammer and retrieve Yammer data.

So first you need to create a Yammer App, you can create it from https://www.yammer.com/client_applications. And click on the Register New App button, which will show a popup like this.

Creating a new Yammer App

Make sure the redirect URL is https://localhost:5001/signin-yammer. Once the app is created, you will be redirected to a page like this

Creating a new Yammer App

Where you will be able to see the client id and client secret. Next you need to create an ASP.NET Core MVC project, I am using OAuth provider for authentication. So here is the code for enabling OAuth authentication in ASP.NET Core.

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
    .AddCookie(o => o.LoginPath = new PathString("/login"))
    .AddOAuth("Yammer-Token", "Yammer", o =>
    {
        o.ClientId = Configuration["Yammer:clientid"];
        o.ClientSecret = Configuration["Yammer:clientsecret"];
        o.CallbackPath = new PathString("/signin-yammer");
        o.AuthorizationEndpoint = YammerAccountDefaults.AuthorizationEndpoint;
        o.TokenEndpoint = YammerAccountDefaults.TokenEndpoint;
        o.SaveTokens = true;
    });

    services.AddMvc();
}

And here is the code to show authentication dialog.

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseAuthentication();
    app.Map("/login", builder =>
    {
        builder.Run(async context =>
        {
            await context.ChallengeAsync("Yammer-Token", new AuthenticationProperties() { RedirectUri = "/" });
            return;
        });
    });

    app.Map("/logout", builder =>
    {
        builder.Run(async context =>
        {
            await context.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
            context.Response.Redirect("/");
        });
    });
}

Now you can run the app, click on the Login button, which will redirect to Yammer Authentication dialog.

Yammer authentication dialog

Once you provide the credentials and click Login, you will be redirected to the authorization dialog, like this.

Yammer authorization dialog

Once you click Ok, you will be redirected back to your application and you can get details about user from current user endpoint, using following code.

options.Events = new OAuthEvents()
{
    OnCreatingTicket = async context =>
    {
        var request = new HttpRequestMessage(HttpMethod.Get, context.Options.UserInformationEndpoint);
        request.Headers.Add("Authorization", $"Bearer {context.AccessToken}");
        var response = await context.Backchannel.SendAsync(request, context.HttpContext.RequestAborted);
        response.EnsureSuccessStatusCode();
        var userObject = JObject.Parse(await response.Content.ReadAsStringAsync());
        var userId = userObject.SelectToken("id").Value<long>();
        var fullName = userObject.SelectToken("full_name").Value<string>();
        if (!string.IsNullOrEmpty(userId.ToString()))
        {
            context.Identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, userId.ToString(), ClaimValueTypes.String, context.Options.ClaimsIssuer));
        }
        if (!string.IsNullOrEmpty(fullName))
        {
            context.Identity.AddClaim(new Claim(ClaimTypes.Name, fullName, ClaimValueTypes.String, context.Options.ClaimsIssuer));
        }
    }
};

But I got an error like this instead of getting the call in OnCreatingTicket event.

Yammer Authentication Exception

From the stack trace I am able to find that, it is thrown from OAuthTokenResponse class constructor, which is getting created in ExchangeCodeAsync method. Since ASP.NET Core is Open Source (Thank you Microsoft), I am able to look into the source code and I found Yammer response is different from the other providers, so there is no other option than writing custom authentication provider for Yammer. So I wrote a Yammer provider, which inherits from OAuthHandler class. And I am overriding the ExchangeCodeAsync so that it the proper JObject can be available for the OAuthTokenResponse constructor. So here is the implementation.

protected override async Task<OAuthTokenResponse> ExchangeCodeAsync(string code, string redirectUri)
{
    var tokenRequestParameters = new Dictionary<string, string>()
    {
        { "client_id", Options.ClientId },
        { "redirect_uri", redirectUri },
        { "client_secret", Options.ClientSecret },
        { "code", code }
    };

    var requestContent = new FormUrlEncodedContent(tokenRequestParameters);

    var requestMessage = new HttpRequestMessage(HttpMethod.Post, Options.TokenEndpoint);
    requestMessage.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    requestMessage.Content = requestContent;
    var response = await Backchannel.SendAsync(requestMessage, Context.RequestAborted);
    if (response.IsSuccessStatusCode)
    {
        var payloadObject = JObject.Parse(await response.Content.ReadAsStringAsync());
        var payload = new JObject
        {
            ["access_token"] = payloadObject.Property("access_token").Value["token"],
            ["token_type"] = "code",
            ["refresh_token"] = payloadObject.Property("access_token").Value["token"],
            ["expires_in"] = payloadObject.Property("access_token").Value["expires_at"]
        };

        return OAuthTokenResponse.Success(payload);
    }
    else
    {
        var error = new StringBuilder();
        error.Append("OAuth token endpoint failure: ");
        error.Append("Status: " + response.StatusCode + ";");
        error.Append("Headers: " + response.Headers.ToString() + ";");
        error.Append("Body: " + await response.Content.ReadAsStringAsync() + ";");
        return OAuthTokenResponse.Failed(new Exception(error.ToString()));
    }
}

And here is my updated ConfigureServices method.

services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
.AddCookie(o => o.LoginPath = new PathString("/login"))
.AddYammer("Yammer-Auth", options =>
{
    options.ClientId = Configuration["Yammer:clientid"];
    options.ClientSecret = Configuration["Yammer:clientsecret"];
    options.CallbackPath = "/signin-yammer";
    options.SaveTokens = true;
    options.Events = new OAuthEvents()
    {
        OnCreatingTicket = async context =>
        {
            var request = new HttpRequestMessage(HttpMethod.Get, context.Options.UserInformationEndpoint);
            request.Headers.Add("Authorization", $"Bearer {context.AccessToken}");
            var response = await context.Backchannel.SendAsync(request, context.HttpContext.RequestAborted);
            response.EnsureSuccessStatusCode();
            var userObject = JObject.Parse(await response.Content.ReadAsStringAsync());
            var userId = userObject.SelectToken("id").Value<long>();
            var fullName = userObject.SelectToken("full_name").Value<string>();
            if (!string.IsNullOrEmpty(userId.ToString()))
            {
                context.Identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, userId.ToString(), ClaimValueTypes.String, context.Options.ClaimsIssuer));
            }
            if (!string.IsNullOrEmpty(fullName))
            {
                context.Identity.AddClaim(new Claim(ClaimTypes.Name, fullName, ClaimValueTypes.String, context.Options.ClaimsIssuer));
            }
        }
    };
});

Now it is getting redirected back to our app, when authorization is completed, and on OnCreatingTicket event, I am updating the identity with userId and full name, so that we can use it in the App. Here is the screenshot of the app running on my machine.

Application with Logged in user name

Source code of the application is available in Github

Happy Programming :)


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Copyright © 2018 - Anuraj P. Blog content licensed under the Creative Commons CC BY 2.5 | Unless otherwise stated or granted, code samples licensed under the MIT license. This is a personal blog. The opinions expressed here represent my own and not those of my employer. Hosted with ❤ by GitHub