Ory is the largest open source community in the world for cloud software application security. We maintain advanced open source security software solving authentication, authorization, access control, application network security, and delegation. Ory implements a variety of industry and best-practice standards including OAuth 2.0 / OAuth 2.1, OpenID Connect, Zero Trust Networking, Google Zanzibar Policy Framework, FIDO2 U2F, WebAuthn, TOTP, and more.

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I'm confused on login challenges. Where are those generated? They don't seem optional.

Login challenge is just a unique ID of specific login request so you can refer to it.

Right but who generates it? I've cloned the login/consent app. When I hit the login page, it shows a 404 from hydra admin. It's trying to look up the login challenge to find session information but I haven't logged in before so none will exist yet.

A login challenge is generated by hydra, right before it redirects to the consent app to complete it.

You don't have to have "logged in before"

Have you read this?
<https://www.ory.sh/hydra/docs/concepts/login>