How to build SAML sign-in with .NET Core (Razor Pages) and Logto

December 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 SAML sign-in experience (user authentication) with .NET Core (Razor Pages) and Logto.

Prerequisites

A running Logto instance. Check out the introduction page to get started.
Basic knowledge of .NET Core (Razor Pages).
A usable SAML 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 (Razor Pages)" 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

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 the handler methods to your PageModel, for example:

Pages/Index.cshtml.cs
public class IndexModel : PageModel
{
  public async Task OnPostSignInAsync()
  {
    await HttpContext.ChallengeAsync(new AuthenticationProperties
    {
      RedirectUri = "/"
    });
  }

  public async Task OnPostSignOutAsync()
  {
    await HttpContext.SignOutAsync(new AuthenticationProperties
    {
      RedirectUri = "/"
    });
  }
}

Then, add the buttons to your Razor page:

Pages/Index.cshtml
<p>Is authenticated: @User.Identity?.IsAuthenticated</p>
<form method="post">
  @if (User.Identity?.IsAuthenticated == true) {
    <button type="submit" asp-page-handler="SignOut">Sign out</button>
  } else {
    <button type="submit" asp-page-handler="SignIn">Sign in</button>
  }
</form>

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

Test your integration:

Open your .NET Core (Razor Pages) 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 SAML 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 "SAML" 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 SAML app

Let's go through configurations of SAML connector.

Before we kicking off, you can go to a social identity provider which supports SAML protocol and create your own account. Okta, OneLogin, Salesforce and some other platforms support authentication based on SAML protocol.

If your IdP mandate the encryption of SAML assertion and receiving of signed authentication requests, you should generate your private key and corresponding certificate using RSA algorithm. Keep the private key for your SP use and upload the certificate to IdP.

You also need to configure the ACS (Assertion Consumer Service) URL as ${your_logto_origin}/api/authn/saml/${connector_id} to handle IdP's SAML assertion. Where you can find your connectorId at SAML connector's details page in Logto's Admin Console.

ℹ️ Note

Per current Logto's design, we only support Redirect-binding for sending authentication request and POST-binding for receiving SAML assertion. Although this sounds not cool, but we believe that the current design can handle most of your use cases. If you have any problems, feel free to reach out!

Configure SAML connector (SP)

In this section, we will introduce each attribute in detail.

entityID `Required`

entityID (i.e. issuer) is Entity identifier. It is used to identify your entity (SAML SP entity), and match the equivalence in each SAML request/response.

signInEndpoint `Required`

The IdP's endpoint that you send SAML authentication requests to. Usually, you can find this value in IdP details page (i.e. IdP's SSO URL or Login URL).

x509Certificate `Required`

The x509 certificate generated from IdPs private key, IdP is expected to have this value available.

The content of the certificate comes with -----BEGIN CERTIFICATE----- header and -----END CERTIFICATE----- tail.

idpMetadataXml `Required`

The field is used to place contents from your IdP metadata XML file.

ℹ️ Note

The XML parser we are using does not support customized namespace. If the IdP metadata comes with namespace, you should manually remove them. For namespace of XML file, see reference.

assertionConsumerServiceUrl `Required`

The assertion consumer service (ACS) URL is the SP's endpoint to receive IdP's SAML Assertion POST requests. As we mentioned in previous part, it is usually configured at IdP settings but some IdP get this value from SAML authentication requests, we hence also add this value as a REQUIRED field. It's value should look like ${your_logto_origin}/api/authn/saml/${connector_id}.

signAuthnRequest

The boolean value that controls whether SAML authentication request should be signed, whose default value is false.

encryptAssertion

encryptAssertion is a boolean value that indicates if IdP will encrypt SAML assertion, with default value false.

ℹ️ Note

signAuthnRequest and encryptAssertion attributes should align with corresponding parameters of IdP setting, otherwise error will be thrown to show that configuration does not match. All SAML responses need to be signed.

requestSignatureAlgorithm

This should be aligned with the signature algorithms of IdP so that Logto can verify the signature of the SAML assertion. Its value should be either http://www.w3.org/2000/09/xmldsig#rsa-sha1, http://www.w3.org/2001/04/xmldsig-more#rsa-sha256 or http://www.w3.org/2001/04/xmldsig-more#rsa-sha512 and the default value is http://www.w3.org/2001/04/xmldsig-more#rsa-sha256.

messageSigningOrder

messageSigningOrder indicates the signing and encrypting order of IdP, it's value should be either sign-then-encrypt or encrypt-then-sign and the default value is sign-then-encrypt.

privateKey and privateKeyPass

privateKey is an OPTIONAL value and is required when signAuthnRequest is true.

privateKeyPass is the password you've set when creating privateKey, required when necessary.

If signAuthnRequest is true, the corresponding certificate generated from privateKey is required by IdP for checking the signature.

encPrivateKey and encPrivateKeyPass

encPrivateKey is an OPTIONAL value and is required when encryptAssertion is true.

encPrivateKeyPass is the password you've set when creating encPrivateKey, required when necessary.

If encryptAssertion is true, the corresponding certificate generated from encPrivateKey is required by IdP for encrypting SAML assertion.

ℹ️ Note

For keys and certificates generation, openssl is a wonderful tool. Here is sample command line that might be helpful:
openssl genrsa -passout pass:${privateKeyPassword} -out ${encryptPrivateKeyFilename}.pem 4096
openssl req -new -x509 -key ${encryptPrivateKeyFilename}.pem -out ${encryptionCertificateFilename}.cer -days 3650
privateKey and encPrivateKey files are enforced to be encoded in pkcs1 scheme as pem string, which means the private key files should start with -----BEGIN RSA PRIVATE KEY----- and end with -----END RSA PRIVATE KEY-----.

nameIDFormat

nameIDFormat is an OPTIONAL attribute that declares the name id format that would respond. The value can be among urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified, urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress, urn:oasis:names:tc:SAML:1.1:nameid-format:X509SubjectName, urn:oasis:names:tc:SAML:2.0:nameid-format:persistent and urn:oasis:names:tc:SAML:2.0:nameid-format:transient, and the default value is urn:oasis:names:tc:SAML:2.0:nameid-format:unspecified.

timeout

timeout is the time tolerance for time validation, since the time between your SP entity and IdP entity could be different and network connection may also bring some delay. The unit is in millisecond, and the default value is 5000 (i.e. 5s).

profileMap

Logto also provide a profileMap field that users can customize the mapping from the social vendors' profiles which are usually not standard. Each profileMap keys is Logto's standard user profile field name and corresponding value should be social profiles field name. In current stage, Logto only concern 'id', 'name', 'avatar', 'email' and 'phone' from social profile, only 'id' is REQUIRED and others are optional fields.

Config types

Name	Type	Required	Default Value
signInEndpoint	string	true
x509certificate	string	true
idpMetadataXml	string	true
entityID	string	true
assertionConsumerServiceUrl	string	true
messageSigningOrder	`encrypt-then-sign` \| `sign-then-encrypt`	false	`sign-then-encrypt`
requestSignatureAlgorithm	`http://www.w3.org/2000/09/xmldsig#rsa-sha1` \| `http://www.w3.org/2001/04/xmldsig-more#rsa-sha256` \| `http://www.w3.org/2001/04/xmldsig-more#rsa-sha512`	false	`http://www.w3.org/2001/04/xmldsig-more#rsa-sha256`
signAuthnRequest	boolean	false	false
encryptAssertion	boolean	false	false
privateKey	string	false
privateKeyPass	string	false
nameIDFormat	`urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified` \| `urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress` \| `urn:oasis:names:tc:SAML:1.1:nameid-format:X509SubjectName` \| `urn:oasis:names:tc:SAML:2.0:nameid-format:persistent` \| `urn:oasis:names:tc:SAML:2.0:nameid-format:transient`	false	`urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified`
timeout	number	false	5000
profileMap	ProfileMap	false

ProfileMap fields	Type	Required	Default value
id	string	false	id
name	string	false	name
avatar	string	false	avatar
email	string	false	email
phone	string	false	phone

Reference

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 SAML 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 SAML sign-in, which may increase your conversion rate.

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

Save changes

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

Testing and Validation

Return to your .NET Core (Razor Pages) app. You should now be able to sign in with SAML. 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​

Regarding redirect-based sign-in​

Configure redirect URIs​

Change the default paths​

Implement sign-in/sign-out buttons​

Add SAML connector​

Set up Standard SAML app​

Create social IdP's account and register SAML application (IdP)​

Configure SAML connector (SP)​

entityID Required​

signInEndpoint Required​

x509Certificate Required​

idpMetadataXml Required​

assertionConsumerServiceUrl Required​

signAuthnRequest​

encryptAssertion​

requestSignatureAlgorithm​

messageSigningOrder​

privateKey and privateKeyPass​

encPrivateKey and encPrivateKeyPass​

nameIDFormat​

timeout​

profileMap​

Config types​

Reference​

Save your configuration​

Enable SAML connector in Sign-in Experience​

Testing and Validation​

Further readings​