Authentication and Customers

Purchase does not replace application auth. The example begins with normal sign-in and sign-up pages, then maps authenticated users into billing customers.

Relevant files:

• sign-in page
• sign-up page
• auth form
• auth session helpers

Auth flow

The client form uses Better Auth:

const result =
  props.mode === "sign-up"
    ? await authClient.signUp.email({
        email,
        password,
        name,
        callbackURL: "/workspace"
      })
    : await authClient.signIn.email({
        email,
        password,
        callbackURL: "/workspace"
      })

Session to customer mapping

The key idea is that billing starts from app identity, not provider identity.

The example converts the session into an app-owned customer shape with sessionUser(...), then passes that user into Purchase runtime helpers.

Why this matters

This keeps:

• auth ownership in the app
• customer ids stable across providers
• commercial state aligned with the rest of product state