Advanced Security: Configuring OIDC and OAuth Flows
In this lesson, you will learn how to configure OpenID Connect (OIDC) and OAuth 2.0 flows to secure your Blazor applications against modern identity threats.
When building Blazor applications, we often move beyond simple cookie-based authentication toward delegated identity management using OIDC and OAuth 2.0. Instead of handling passwords directly, your application acts as a client that delegates authentication to an Identity Provider (IdP) like Duende IdentityServer, Auth0, or Entra ID.
The Authorization Code Flow with PKCE
For Blazor, the gold standard is the Authorization Code Flow with PKCE (Proof Key for Code Exchange). Unlike older flows, PKCE prevents "code injection" attacks by requiring the client to prove it is the same entity that initiated the request.
In your Program.cs, you configure the OIDC handler to bridge your Blazor app with your IdP. Here is a simplified implementation of how you configure these options:
builder.Services.AddOidcAuthentication(options =>
{
builder.Configuration.Bind("Oidc", options.ProviderOptions);
options.ProviderOptions.ResponseType = "code"; // Enforce Auth Code Flow
options.ProviderOptions.DefaultScopes.Add("openid");
options.ProviderOptions.DefaultScopes.Add("profile");
// PKCE is enabled by default in modern Blazor OIDC templates
});
Why this matters
By using OIDC, your application never sees the user's raw credentials. Instead, it receives an Identity Token (for user info) and an Access Token (for API calls).
A common pitfall in "Advanced Security" is failing to restrict the audience of your tokens. Always ensure that your appsettings.json includes the correct Authority and ClientId. Furthermore, when the user logs in, the Blazor RemoteAuthenticationState maintains the session lifecycle. If you are using Blazor WebAssembly, these tokens are often stored in memory; if you are using Blazor Server, the state is managed via secure, encrypted cookies that handle the OIDC handshake behind the scenes.
By standardizing on these flows, you ensure that your application is resilient, follows industry best practices, and minimizes the attack surface by never handling sensitive user passwords directly within your component logic.
Key Takeaway: Always use Authorization Code Flow with PKCE to securely delegate authentication to an external Identity Provider, keeping raw credentials out of your Blazor application.