The module's test provider moves into `package:halkyon_oidc_server/testing.dart`,
so a host tests its own sign-in against the module's real checks rather than
a copy: `TestKey` makes and publishes an RSA key and signs ID tokens with
headers written by hand (no `typ`, as SimpleLogin's), and `FakeProvider`
answers discovery, the keys and the token endpoint through an HTTP client
the host hands the module. `FakeProvider.simpleLogin` has SimpleLogin's
issuer and endpoints, without PKCE, as the preset expects; a test now signs
in through the preset end to end. pointycastle, already in the lock through
dart_jsonwebtoken, becomes a dependency for it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>