App slugs were a compile-time union of four names. That was fine while every app
was ours and it blocks what Heimdall is for: an app it has never heard of,
running on someone else's machine, registering against a self-hosted instance
without forking and rebuilding the auth authority. A creator self-hosting
Erycina alongside Heimdall would otherwise maintain a patched auth server
forever.
AppSlug is now a string, which it always was on the wire; the union was a
narrowing the type system could enforce only because the set was closed.
Membership moved from appSlugs.includes to the registry, and where no store is
reachable — the offline token verifier is the case that matters — it is a shape
check, isAppSlug, rather than a false claim to know what exists. A host app
verifying its own tokens should compare aud against its own slug, which it knows
and Heimdall's built-in list does not.
Registration is data end to end. Storage carries the profile and a hash of the
client secret rather than the secret. Built-in profiles resolve first and their
slugs are refused at registration, in both places, so a registration cannot
shadow a shipped app and inherit its audience.
POST /v1/apps answers in the RFC 7591 shape so an ordinary OAuth client library
can read it, returning client_secret exactly once. It is gated on an operator
secret and closed entirely until one is configured: an open registration
endpoint on an OAuth provider lets anyone create a client that starts Discord
and Patreon flows under the instance's identity, which is a phishing surface
wearing the operator's name. A fresh instance is not accidentally open.
Redirect URIs are validated rather than stored as given. They are where an
authorization code is delivered, so a permissive one is a token-theft primitive:
absolute, no fragment, https unless loopback.
Six call sites assumed an app profile always exists. They now answer 404 for an
app nobody registered, and claim issuance refuses outright rather than signing a
token whose audience no verifier can resolve.
108 tests pass, 34 of them new. Zero type errors.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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