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How Auth0 works

Auth0 identity provider - token issuance and validation as a third-party dependency. Adds external auth latency; priced per plan (MAU tiers).

Auth0 is "authentication as a service": instead of building login, you redirect users to Auth0, it proves who they are (password, Google, corporate SSO, MFA), and sends them back with a signed token your app trusts. It’s the standard OAuth2/OIDC dance, run by someone else, so you never store passwords or reinvent identity.

What you will learn

What does a hosted Identity Provider do, and why outsource auth?
How does the OAuth2/OIDC redirect flow actually work?
What are ID vs access tokens, and how does your app use them?
How does Auth0 connect to social and enterprise identities?

Authentication as a service

Auth0 is a managed Identity Provider (IdP). Your application delegates login to it: Auth0 handles credentials, MFA, account recovery, and bot/attack protection, and tells your app the result with a cryptographically signed token.

The OAuth2 / OIDC flow

The common pattern is Authorization Code flow with OpenID Connect: your app redirects to Auth0; the user authenticates; Auth0 redirects back with a short-lived code; your app exchanges that code for tokens. The password never passes through your servers.

OIDC is the identity layer on top of OAuth2, it standardises how the user’s identity is returned (in the ID token).

ID tokens vs access tokens

Auth0 issues JWT tokens. The ID token tells your app who the user is (their profile/claims). The access token is what your app sends to your API to prove the user may call it. Your API verifies the token’s signature and claims, no session lookup needed.

Connections and extensibility

Auth0 connections plug in identity sources: username/password databases, social logins (Google, GitHub), and enterprise SSO (SAML, OIDC, Active Directory). You flip on a provider rather than integrating each one yourself. Actions let you run custom logic during login (enrich tokens, enforce rules).

⚓ B2C apps wanting social login, B2B SaaS needing enterprise SSO, and anyone avoiding building identity from scratch.

Auth0 vs Cognito, how do they compare?

Both are managed identity providers issuing JWTs. Cognito is AWS-native and integrates tightly with AWS (and Identity Pools for AWS credentials). Auth0 is platform-agnostic with a richer extensibility/enterprise-SSO feature set and developer experience, at a different price model. Choose by ecosystem, features, and cost.

Flashcards

What does Auth0 let you stop building yourself?: Authentication: login, MFA, account recovery, social/enterprise SSO. You delegate to the hosted IdP and trust its signed tokens.
Outline the Authorization Code (OIDC) flow.: App redirects to Auth0 → user authenticates → Auth0 redirects back with a code → app exchanges it for tokens. Password never hits your server.
ID token vs access token?: ID token = who the user is (profile/claims). Access token = sent to your API to prove the user may call it.
What must your API check on a bearer token each request?: Signature, issuer, audience, and expiry, tokens are bearer credentials, so validate them every time (and keep lifetimes short).
How do you add Google login or enterprise SSO in Auth0?: Enable a connection for that identity source (social or SAML/OIDC enterprise), rather than integrating each provider yourself.

Sources

Open the SysPad canvas · Official Auth0 documentation