Human: Hi! I keep hearing about OpenID Connect at work. Can you explain what it is and why we'd use it instead of just regular passwords?

Assistant: OpenID Connect (OIDC) is an identity layer built on top of OAuth 2.0 that allows applications to verify who you are without handling your password directly. Think of it like showing your driver's license to prove your age at a bar - the bar doesn't need to know your home address or store a copy, they just need to verify you're over 21 from a trusted source.

Instead of every application storing and managing passwords (which is risky), OIDC lets users authenticate with an identity provider they trust - like Google, Microsoft, or your company's SSO system. The application gets proof that you are who you claim to be, along with some basic profile information if needed.

The main benefits are improved security (fewer places storing credentials means fewer breach points), better user experience (single sign-on across multiple apps), and reduced liability for application developers who don't have to manage password security themselves.

Human: Okay, that makes sense. So how does the actual flow work? Like, what happens when I click "Sign in with Google" on a website?

Assistant: Great question! Here's what happens behind the scenes:

When you click "Sign in with Google," you trigger what's called the Authorization Code Flow. The website (called the Relying Party or client) redirects your browser to Google's authorization server with a request that includes information like the client's ID and what information it wants to access.

You then see Google's login page where you authenticate with your Google credentials. This is crucial - you're logging into Google directly, not giving your password to the website. After you successfully log in, Google asks if you consent to share certain information with the website.

Once you approve, Google redirects you back to the website with an authorization code. The website then exchanges this code (along with a client secret that only it knows) directly with Google's server for tokens. The most important one is the ID token, which is a cryptographically signed piece of data (a JWT) that proves your identity. There's also typically an access token if the app needs to access additional resources on your behalf.

The website validates the ID token's signature to ensure it really came from Google, checks that it hasn't expired, and then knows who you are!

Human: You mentioned an ID token and a JWT. What exactly is in that token?

Assistant: An ID token is a JSON Web Token (JWT), which is essentially a tamper-proof package of information about you. It has three parts separated by dots: a header, a payload, and a signature.

The payload (the middle part) contains claims - statements about you and the authentication event. Standard claims include:

• iss (issuer): Who created the token, like "https://accounts.google.com"
• sub (subject): Your unique identifier at that identity provider
• aud (audience): Which application this token is intended for
• exp (expiration): When the token expires
• iat (issued at): When the token was created
• nonce: A random value to prevent replay attacks

It can also include profile information like your email, name, or profile picture URL if you consented to share those.

The signature at the end is what makes this secure. The identity provider signs the token using a private key, and the application can verify this signature using the provider's public key. This proves the token wasn't tampered with and really came from Google (or whoever the provider is). The application never has to call back to verify - it can check the signature locally, which makes OIDC quite efficient.

Human: What's the difference between the ID token and the access token you mentioned?

Assistant: Excellent question - they serve different purposes!

The ID token is all about identity. It tells the application who you are. Think of it like your passport - it proves your identity. The application validates it, reads the claims about you, and that's typically the end of its lifecycle. It's meant to be read and validated by the application.

The access token is about authorization and access. It's like a hotel key card - it grants access to specific resources. If the application needs to do things on your behalf (like read your Google Calendar or access your profile information from an API), it uses the access token to make those requests. The application doesn't need to look inside the access token - it just passes it along to the resource server (like Google's API) to prove it has permission.

In pure authentication scenarios (just logging in), you might only use the ID token. But if the application needs ongoing access to your data from the identity provider, it'll also use the access token. There's often a refresh token too, which lets the application get a new access token when the old one expires without making you log in again.

The key distinction: ID token = who you are (authentication), access token = what you can access (authorization).

Human: This is really helpful! Can you show me my login page at https://taggart-tech.com?

Assistant: Yes! Here it is. In fact I'll generate the link right here for you!