Azure B2C with IdentityServer (sign-in only)

Config - HttpDocumentRetriever.cs

using Microsoft.IdentityModel.Protocols;
using System;
using System.IO;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

// Per https://azure.microsoft.com/en-us/documentation/articles/active-directory-b2c-devquickstarts-web-dotnet/

namespace Host.Configuration
{
    class HttpDocumentRetriever : IDocumentRetriever
    {
        private readonly HttpClient _httpClient;

        public HttpDocumentRetriever()
            : this(new HttpClient())
        {
        }

        public HttpDocumentRetriever(HttpClient httpClient)
        {
            if (httpClient == null)
            {
                throw new ArgumentNullException("httpClient");
            }
            _httpClient = httpClient;
        }

        public async Task<string> GetDocumentAsync(string address, CancellationToken cancel)
        {
            if (string.IsNullOrWhiteSpace(address))
            {
                throw new ArgumentNullException("address");
            }
            try
            {
                HttpResponseMessage response = await _httpClient.GetAsync(address, cancel).ConfigureAwait(false);
                response.EnsureSuccessStatusCode();
                return await response.Content.ReadAsStringAsync().ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                throw new IOException("Unable to get document from: " + address, ex);
            }
        }
    }
}

Config - olicyConfigurationManager.cs

using Microsoft.IdentityModel.Protocols;
using System;
using System.IO;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

// Per https://azure.microsoft.com/en-us/documentation/articles/active-directory-b2c-devquickstarts-web-dotnet/

namespace Host.Configuration
{
    class HttpDocumentRetriever : IDocumentRetriever
    {
        private readonly HttpClient _httpClient;

        public HttpDocumentRetriever()
            : this(new HttpClient())
        {
        }

        public HttpDocumentRetriever(HttpClient httpClient)
        {
            if (httpClient == null)
            {
                throw new ArgumentNullException("httpClient");
            }
            _httpClient = httpClient;
        }

        public async Task<string> GetDocumentAsync(string address, CancellationToken cancel)
        {
            if (string.IsNullOrWhiteSpace(address))
            {
                throw new ArgumentNullException("address");
            }
            try
            {
                HttpResponseMessage response = await _httpClient.GetAsync(address, cancel).ConfigureAwait(false);
                response.EnsureSuccessStatusCode();
                return await response.Content.ReadAsStringAsync().ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                throw new IOException("Unable to get document from: " + address, ex);
            }
        }
    }
}

Config - RelyingParties.cs

...

  // This is the SaaS application. I'm just using a normal MVC application to illustrate the point.
  
  new RelyingParty
  {
      Realm = "https://localhost:44320/",
      Enabled = true,
      ReplyUrl = "https://localhost:44320/",
      //TokenType = TokenTypes.Saml2TokenProfile11,
      TokenLifeTime = 1,

      ClaimMappings = new Dictionary<string, string>
      {
          { "sub", ClaimTypes.NameIdentifier },
          { "name", ClaimTypes.Name },
          { "given_name", ClaimTypes.GivenName },
          { "surname", ClaimTypes.Surname },
          { "email", ClaimTypes.Email }
      }
  }
  
  ...
  

IdentityServerExtensions.cs (inside of ConfigureIdentityProviders)

// idsrv3 runs as https://my-pc/idsrv3.Host.Web

// You need to configure B2C yourself

var signUpPolicyId = "B2C_1_Sign-up-email";
var signInPolicyId = "B2C_1_Sign-in-email";
var userProfilePolicyId = "B2C_1_Edit-email";

var clientId = "c3...f1f";
var redirectUri = "https://my-pc/idsrv3.Host.Web/core/external";
            
var OIDCMetadataSuffix = "/.well-known/openid-configuration";

var tenant = "myb2c.onmicrosoft.com";
var aadInstance = "https://login.microsoftonline.com/{0}{1}{2}";

var b2c = new OpenIdConnectAuthenticationOptions
{
    AuthenticationType = "b2c",
    Caption = "Azure B2C",
    SignInAsAuthenticationType = signInAsType,
                
    // These are standard OpenID Connect parameters, with values pulled from web.config
    ClientId = clientId,
    RedirectUri = redirectUri,
    PostLogoutRedirectUri = redirectUri,
    
    Notifications = new OpenIdConnectAuthenticationNotifications
    {
        AuthenticationFailed = AuthenticationFailed,
        RedirectToIdentityProvider = OnRedirectToIdentityProvider,
    },
                
    Scope = "openid",
    ResponseType = "id_token",

    // The PolicyConfigurationManager takes care of getting the correct Azure AD authentication
    // endpoints from the OpenID Connect metadata endpoint.  It is included in the PolicyAuthHelpers folder.
    
    ConfigurationManager = new PolicyConfigurationManager(
    String.Format(CultureInfo.InvariantCulture, aadInstance, tenant, "/v2.0", OIDCMetadataSuffix),
    new string[] { signUpPolicyId, signInPolicyId, userProfilePolicyId }),

};

app.UseOpenIdConnectAuthentication(b2c);

IdentityServerExtensions.cs (new methods)

// Per https://azure.microsoft.com/en-us/documentation/articles/active-directory-b2c-devquickstarts-web-dotnet/

// This notification can be used to manipulate the OIDC request before it is sent.  Here we use it to send the correct policy.
  private static async Task OnRedirectToIdentityProvider(RedirectToIdentityProviderNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
  {
      var policyKey = "b2cpolicy";

      PolicyConfigurationManager mgr = notification.Options.ConfigurationManager as PolicyConfigurationManager;
      if (notification.ProtocolMessage.RequestType == OpenIdConnectRequestType.LogoutRequest)
      {
          // Not handled = sign-in only
          OpenIdConnectConfiguration config = await mgr.GetConfigurationByPolicyAsync(CancellationToken.None, notification.OwinContext.Authentication.AuthenticationResponseRevoke.Properties.Dictionary[policyKey]);
          notification.ProtocolMessage.IssuerAddress = config.EndSessionEndpoint;
      }
      else
      {
          // Policy hard-coded
          OpenIdConnectConfiguration config = await mgr.GetConfigurationByPolicyAsync(CancellationToken.None, "B2C_1_Sign-in-email");
          notification.ProtocolMessage.IssuerAddress = config.AuthorizationEndpoint;
      }
  }

  // Used for avoiding yellow-screen-of-death
  private static Task AuthenticationFailed(AuthenticationFailedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
  {
      notification.HandleResponse();
      notification.Response.Redirect("/Home/Error?message=" + notification.Exception.Message);
      return Task.FromResult(0);
  }
  

http://nzpcmad.blogspot.co.nz/2016/06/azure-b2c-integration-with.html