'Cannot get web app to redirect to Azure AD B2C Sign in Page

I have a Web app in web forms trying to authenticate to an Azure AD B2C tenant. I've set up my B2C tenant, added all the keys in the web.config, i.e.

<add key="ida:ClientId" value="xxxxx"/>
<add key="ida:AadInstance" value="https://login.microsoftonline.com/" />
<add key="ida:Domain" value="xxxxx.onmicrosoft.com" />
<add key="ida:TenantId" value="xxxxx" />
<add key="ida:ClientSecret" value="xxxxx"/>
<add key="ida:PostLogoutRedirectUri" value="https://xxxxx.azurewebsites.net/" />
<add key="ida:SignUpSignInPolicyId" value="B2C_1_SignUpSignIn" />
<add key="ida:EditProfilePolicyId" value="B2C_1_Edit_Profile" />
<add key="ida:ResetPasswordPolicyId" value="B2C_1_Password_Reset" />

The rest of the code (i.e. StartupAuth.cs) I have left as was generated by Visual Studio, i.e. 

private static string clientId = ConfigurationManager.AppSettings["ida:ClientId"];
    private static string aadInstance = ConfigurationManager.AppSettings["ida:AADInstance"];
    private static string tenantId = ConfigurationManager.AppSettings["ida:TenantId"];
    private static string postLogoutRedirectUri = ConfigurationManager.AppSettings["ida:PostLogoutRedirectUri"];

    string authority = aadInstance + tenantId;

    public void ConfigureAuth(IAppBuilder app)
    {
        app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

        app.UseCookieAuthentication(new CookieAuthenticationOptions());

        app.UseOpenIdConnectAuthentication(
            new OpenIdConnectAuthenticationOptions
            {
                ClientId = clientId,
                Authority = authority,
                PostLogoutRedirectUri = postLogoutRedirectUri,

                Notifications = new OpenIdConnectAuthenticationNotifications()
                {
                    AuthenticationFailed = (context) =>
                    {
                        return System.Threading.Tasks.Task.FromResult(0);
                    }
                }

            }
            );

        // This makes any middleware defined above this line run before the Authorization rule is applied in web.config
        app.UseStageMarker(PipelineStage.Authenticate);

If I click the linkbutton which fires this code:

if (!Request.IsAuthenticated)
        {
            HttpContext.Current.GetOwinContext().Authentication.Challenge(
                new AuthenticationProperties { RedirectUri = "/" },
                OpenIdConnectAuthenticationDefaults.AuthenticationType);
        }

then I get taken to a standard MS login page, rather than the one specified in the B2C tenant, with social providers and a sign up link. They are both login.microsoftonline.com, but the querystrings are substantially different. I've been trying variations on all the code for 2 days now with no luck - anything else I have tried comes back with "Response status code does not indicate success: 400 (Bad Request)."

c++sharpasp.netazureauthenticationwebforms


Solution 1:[1]

I understand you need to go to your app dashboard on azure, and turn on app service authentication on Authentication / Authorization option using Azure AD setup.

Solution 2:[2]

Also found this in 2022:-)

InstanceId needs to be your AzureTenantDomain? "Instance": "https://login.microsoftonline.com/" "Instance": "https://[yourAzureB2Csubdomain].b2clogin.com/",

then it can find the Policy related... "SignUpSignInPolicyId": "B2C_1_SignUpSignIn"

or you get the MS Popup

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Mauricio Atanache
Solution 2 Tom Leeson

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