What is OpenID and How to implement on Azure Cloud.

OpenID is an open standard and decentralized authentication protocol that allows users to authenticate with different websites and applications using a single set of credentials, rather than having to create and remember different usernames and passwords for each one. OpenID providers, such as Google, Yahoo, and AOL, offer OpenID authentication services that can be used by websites and applications to authenticate their users.

To implement OpenID on Azure, you can use Azure Active Directory (Azure AD) as an OpenID provider. Azure AD is a fully managed, multi-tenant service that provides identity and access management capabilities for applications running in Azure, as well as for external applications that want to authenticate users from Azure AD.

Here’s an example of how to implement OpenID authentication using Azure AD in a .NET Core web application:

1. Register your application in Azure AD. To do this, go to the Azure portal and navigate to the Azure AD tenant where you want to register your application. Then, go to “App registrations” and click on “New registration”. Give your application a name and set the “Supported account types” to “Accounts in any organizational directory and personal Microsoft accounts”.
2. Configure the redirect URI for your application. This is the URL that Azure AD will redirect to after a user has authenticated. In this example, we’ll use “https://localhost:5001/signin-oidc” as the redirect URI.
3. Add the OpenID Connect middleware to your application. To do this, install the Microsoft.AspNetCore.Authentication.OpenIdConnect package in your application and add the following code to your Startup.cs file:

services.AddAuthentication(options =>
{
    options.DefaultScheme = "Cookies";
    options.DefaultChallengeScheme = "oidc";
})
.AddCookie("Cookies")
.AddOpenIdConnect("oidc", options =>
{
    options.Authority = "https://login.microsoftonline.com/{your tenant id}";
    options.ClientId = "{your client id}";
    options.ClientSecret = "{your client secret}";
    options.ResponseType = "code";
    options.SaveTokens = true;
    options.GetClaimsFromUserInfoEndpoint = true;
    options.Scope.Add("openid");
    options.Scope.Add("profile");
    options.Scope.Add("email");
    options.Scope.Add("offline_access");
    options.Scope.Add("https://{your tenant}.onmicrosoft.com/api/user_impersonation");
    options.CallbackPath = "/signin-oidc";
    options.SignedOutCallbackPath = "/signout-callback-oidc";
    options.RemoteSignOutPath = "/signout-oidc";
});

4. Add the [Authorize] attribute to the controllers or actions that you want to protect with authentication. For example:

[Authorize]
public class HomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
}

5. Run the application and navigate to the protected pages. You should be prompted to sign in with your Azure AD credentials. Once you’ve signed in, you’ll be able to access the protected pages.

This is just a basic example of how to implement OpenID authentication using Azure AD in a .NET Core web application. There are many other scenarios and configurations

that you can implement depending on your specific requirements. For example, you can use Azure AD to authenticate users from external organizations by configuring a federation with their identity provider, or you can use Azure AD B2C as an OpenID provider to authenticate consumers of your application.

Another important aspect to consider when implementing OpenID authentication is the management of user’s access tokens and refresh tokens. Access tokens are short-lived tokens that are issued by the OpenID provider to the application, and can be used to authenticate the user and access protected resources. Refresh tokens, on the other hand, are long-lived tokens that can be used to obtain new access tokens without requiring the user to sign in again.

In the example above, the SaveTokens option is set to true, which means that the OpenID Connect middleware will save the access token and refresh token in the authentication cookie, so they can be used for subsequent requests. However, it’s important to keep in mind that access tokens and refresh tokens should be stored securely and not exposed to the client. One approach to securely store the tokens is to use a token store such as Azure Key Vault.

In summary, OpenID is a powerful authentication protocol that enables users to authenticate with different applications using a single set of credentials, and Azure AD can be used as an OpenID provider to authenticate users in a .NET Core web application. There are many other scenarios and configurations that can be implemented depending on the specific requirements of the application, but it’s important to keep in mind the security of the tokens and the user’s credentials.