How to build OIDC sign-in with .NET Core (MVC) and Logto

November 22, 2024 · 2 min read

The better identity infrastructure for developers

For our new friends

Every app needs authentication and authorization. Logto is an Auth0 alternative designed for modern apps and SaaS products.

In this article, we will go through the steps to quickly build the OIDC sign-in experience (user authentication) with .NET Core (MVC) and Logto.

Prerequisites

A running Logto instance. Check out the get started page if you don't have one.
Basic knowledge of .NET Core (MVC).
A usable OIDC account.

Create an application in Logto

In you browser, open a new tab and enter the link of Logto Admin Console.

Get Started

Once the page is loaded, in the "Get Started" section click the View all link to open the application framework list page.

Choose your application type

Framework List

In the opening modal, scroll to the "Traditional web" section or filter all the available " Traditional web" frameworks using the quick filter checkboxes on the left.

Click the ".NET Core (MVC)" framework card to start creating your application.

Enter application name

Enter the application name, e.g., "Bookstore," and click "Create application."

🎉 Ta-da! You just created your first application in Logto. You'll see a congrats page which includes a detailed integration guide. Follow the guide to see what the experience will be in your application.

Integrate Logto SDK

tip

The following demonstration is built on .NET Core 8.0. The SDK is compatible with .NET 6.0 or higher.
The .NET Core sample projects are available in the GitHub repository.

Installation

Add the NuGet package to your project:

dotnet add package Logto.AspNetCore.Authentication

Add Logto authentication

Open Startup.cs (or Program.cs) and add the following code to register Logto authentication services:

Program.cs
using Logto.AspNetCore.Authentication;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddLogtoAuthentication(options =>
{
  options.Endpoint = builder.Configuration["Logto:Endpoint"]!;
  options.AppId = builder.Configuration["Logto:AppId"]!;
  options.AppSecret = builder.Configuration["Logto:AppSecret"];
});

The AddLogtoAuthentication method will do the following things:

Set the default authentication scheme to LogtoDefaults.CookieScheme.
Set the default challenge scheme to LogtoDefaults.AuthenticationScheme.
Set the default sign-out scheme to LogtoDefaults.AuthenticationScheme.
Add cookie and OpenID Connect authentication handlers to the authentication scheme.

Before we proceed, there are two confusing terms in the .NET Core authentication middleware that we need to clarify:

CallbackPath: The URI that Logto will redirect the user back to after the user has signed in (the "redirect URI" in Logto)
RedirectUri: The URI that will be redirected to after necessary actions have been taken in the Logto authentication middleware.

The sign-in process can be illustrated as follows:

Similarly, .NET Core also has SignedOutCallbackPath and RedirectUri for the sign-out flow.

For the sack of clarity, we'll refer them as follows:

Term we use	.NET Core term
Logto redirect URI	CallbackPath
Logto post sign-out redirect URI	SignedOutCallbackPath
Application redirect URI	RedirectUri

Regarding redirect-based sign-in

This authentication process follows the OpenID Connect (OIDC) protocol, and Logto enforces strict security measures to protect user sign-in.
If you have multiple apps, you can use the same identity provider (Logto). Once the user signs in to one app, Logto will automatically complete the sign-in process when the user accesses another app.

To learn more about the rationale and benefits of redirect-based sign-in, see Logto sign-in experience explained.

Configure redirect URIs

note

In the following code snippets, we assume your app is running on http://localhost:3000/.

First, let's configure the Logto redirect URI. Add the following URI to the "Redirect URIs" list in the Logto application details page:

http://http://localhost:3000//Callback

To configure the Logto post sign-out redirect URI, add the following URI to the "Post sign-out redirect URIs" list in the Logto application details page:

http://http://localhost:3000//SignedOutCallback

Change the default paths

The Logto redirect URI has a default path of /Callback, and the Logto post sign-out redirect URI has a default path of /SignedOutCallback.

You can leave them as are if there's no special requirement. If you want to change it, you can set the CallbackPath and SignedOutCallbackPath property for LogtoOptions:

Program.cs
builder.Services.AddLogtoAuthentication(options =>
{
  // Other configurations...
  options.CallbackPath = "/Foo";
  options.SignedOutCallbackPath = "/Bar";
});

Remember to update the value in the Logto application details page accordingly.

Implement sign-in/sign-out buttons

First, add actions methods to your Controller, for example:

Controllers/HomeController.cs
public class HomeController : Controller
{
  public IActionResult SignIn()
  {
    // This will redirect the user to the Logto sign-in page.
    return Challenge(new AuthenticationProperties { RedirectUri = "/" });
  }

  // Use the `new` keyword to avoid conflict with the `ControllerBase.SignOut` method
  new public IActionResult SignOut()
  {
    // This will clear the authentication cookie and redirect the user to the Logto sign-out page
    // to clear the Logto session as well.
    return SignOut(new AuthenticationProperties { RedirectUri = "/" });
  }
}

Then, add the links to your View:

Views/Home/Index.cshtml
<p>Is authenticated: @User.Identity?.IsAuthenticated</p>
@if (User.Identity?.IsAuthenticated == true) {
  <a asp-controller="Home" asp-action="SignOut">Sign out</a>
} else {
  <a asp-controller="Home" asp-action="SignIn">Sign in</a>
}

It will show the "Sign in" link if the user is not authenticated, and show the "Sign out" link if the user is authenticated.

Test your integration

Open your .NET Core (MVC) app to test if the integration works. When you click the "Sign In" button, the page should be redirected to a Logto sign-in page, and you should be able to create a new account by entering username and password and complete the sign-in process.

Add OIDC connector

To add a social connector, go to the "Connector" tab in the Admin Console, then click on "Social connectors". From there, click "Add social connector".

In the openning modal, select "OIDC" and click "Next".

On the next page, you will see a two-column layout with the README content on the left and configuration on the right.

Feel free to follow the README file in place or read the following section to complete the configuration process. If you follow the in-place guide, you can skip the next section.

Set up Standard OIDC app

Create your OIDC app

When you open this page, we believe you already know which social identity provider you want to connect to. The first thing to do is to confirm that the identity provider supports the OIDC protocol, which is a prerequisite for configuring a valid connector. Then, follow the identity provider's instructions to register and create the relevant app for OIDC authorization.

Configure your connector

We ONLY support "Authorization Code" grant type for security consideration and it can perfectly fit Logto's scenario.

clientId and clientSecret can be found at your OIDC apps details page.

clientId: The client ID is a unique identifier that identifies the client application during registration with the authorization server. This ID is used by the authorization server to verify the identity of the client application and to associate any authorized access tokens with that specific client application.

clientSecret: The client secret is a confidential key that is issued to the client application by the authorization server during registration. The client application uses this secret key to authenticate itself with the authorization server when requesting access tokens. The client secret is considered confidential information and should be kept secure at all times.

scope: The scope parameter is used to specify the set of resources and permissions that the client application is requesting access to. The scope parameter is typically defined as a space-separated list of values that represent specific permissions. For example, a scope value of "read write" might indicate that the client application is requesting read and write access to a user's data.

You are expected to find authorizationEndpoint, tokenEndpoint, jwksUri and issuer as OpenID Provider's configuration information. They should be available in social vendor's documentation.

authenticationEndpoint: This endpoint is used to initiate the authentication process. The authentication process typically involves the user logging in and granting authorization for the client application to access their resources.

tokenEndpoint: This endpoint is used by the client application to obtain an id token that can be used to access the requested resources. The client application typically sends a request to the token endpoint with a grant type and authorization code to receive an id token.

jwksUri: This is the URL endpoint where the JSON Web Key Set (JWKS) of the social identity provider (IdP for short) can be obtained. The JWKS is a set of cryptographic keys that the IdP uses to sign and verify JSON Web Tokens (JWTs) that are issued during the authentication process. The jwksUri is used by the relying party (RP) to obtain the public keys used by the IdP to sign the JWTs, so the RP can verify the authenticity and integrity of the JWTs received from the IdP.

issuer: This is the unique identifier of the IdP that is used by the RP to verify the JWTs received from the IdP. It is included in the JWTs as the iss claim (Id token is always a JWT). The issuer value should match the URL of the IdP's authorization server, and it should be a URI that the RP trusts. When the RP receives a JWT, it checks the iss claim to ensure that it was issued by a trusted IdP, and that the JWT is intended for use with the RP.

Together, jwksUri and issuer provide a secure mechanism for the RP to verify the identity of the end-user during the authentication process. By using the public keys obtained from the jwksUri, the RP can verify the authenticity and integrity of the JWTs issued by the IdP. The issuer value ensures that the RP only accepts JWTs that were issued by a trusted IdP, and that the JWTs are intended for use with the RP.

Since an authentication request is always required, an authRequestOptionalConfig is provided to wrap all optional configs, you can find details on OIDC Authentication Request. You may also find that nonce is missing in this config. Since nonce should identical for each request, we put the generation of nonce in code implementation. So do not worry about it! Previously mentioned jwksUri and issuer are also included in idTokenVerificationConfig.

You may be curious as to why a standard OIDC protocol supports both the implicit and hybrid flows, yet the Logto connector only supports the authorization flow. It has been determined that the implicit and hybrid flows are less secure than the authorization flow. Due to Logto's focus on security, it only supports the authorization flow for the highest level of security for its users, despite its slightly less convenient nature.

responseType and grantType can ONLY be FIXED values with "Authorization Code" flow, so we make them optional and default values will be automatically filled.

ℹ️ Note

For all flow types, we provided an OPTIONAL customConfig key to put your customize parameters. Each social identity provider could have their own variant on OIDC standard protocol. If your desired social identity provider strictly stick to OIDC standard protocol, the you do not need to care about customConfig.

Config types

Name	Type	Required
scope	string	True
clientId	string	True
clientSecret	string	True
authorizationEndpoint	string	True
tokenEndpoint	string	True
idTokenVerificationConfig	IdTokenVerificationConfig	True
authRequestOptionalConfig	AuthRequestOptionalConfig	False
customConfig	{ [key: string]: string }	False

AuthRequestOptionalConfig properties	Type	Required
responseType	string	False
tokenEndpoint	string	False
responseMode	string	False
display	string	False
prompt	string	False
maxAge	string	False
uiLocales	string	False
idTokenHint	string	False
loginHint	string	False
acrValues	string	False

IdTokenVerificationConfig properties	Type	Required
jwksUri	string	True
issuer	string \| string[]	False
audience	string \| string[]	False
algorithms	string[]	False
clockTolerance	string \| number	False
crit	{ [key: string]: string \| boolean }	False
currentDate	Date	False
maxTokenAge	string \| number	False
subject	string	False
typ	string	False

See here to find more details about IdTokenVerificationConfig.

Save your configuration

Double check you have filled out necessary values in the Logto connector configuration area. Click "Save and Done" (or "Save changes") and the OIDC connector should be available now.

Switch to the "Sign-in experience" tab, then click the "Sign-up and sign-in" tab.

note

If it's the first time you enter the tab, you will see a quick introduction about Sign-in Experience and its basic configuration.

Sign-in Experience tab

Select "None" for the "Sign-up identifier" to provide minimum sign-up effort for OIDC sign-in, which may increase your conversion rate.

In the "Social sign-in" section, add "Add Social Connector" and choose "OIDC". Then you should be able to see a button with text "Continue with OIDC" in the preview section.

Save changes

Finally, click "Save changes" on the bottom right corner.

Testing and Validation

Return to your .NET Core (MVC) app. You should now be able to sign in with OIDC. Enjoy!

Create an application in Logto​

Choose your application type​

Enter application name​

Integrate Logto SDK​

Installation​

Add Logto authentication​

Sign-in and sign-out flows​

Configure redirect URIs​

Change the default paths​

Implement sign-in/sign-out buttons​

Add OIDC connector​

Set up Standard OIDC app​

Create your OIDC app​

Configure your connector​

Config types​

Save your configuration​

Enable OIDC connector in Sign-in Experience​

Testing and Validation​

Further readings​