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fix(app): GitHub sign-in on Linux and Windows waits for the browser

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Signing in with GitHub on Linux ended in "Unable to connect" at 127.0.0.1:43823 after authorizing. flutter_web_auth_2 (v5.1.0, unchanged on its master) ends every pending sign-in when the app is resumed. That suits mobile, where coming back without finishing means giving up, but on the desktop the window regaining focus resumes the app, and the package's loopback server closed before GitHub sent the browser back. FluffyChat's issue #3341 and the package's #171 report the same.

The app now puts its own Linux and Windows implementation behind the package's platform interface (LoopbackWebAuth): the system browser and a loopback address, as RFC 8252 recommends, waiting until GitHub answers, the person cancels, or five minutes pass. It listens on 127.0.0.1 only and answers only the callback's path. Serverpod's PKCE and state check stay in use. There, the account dialog shows "Continue in your browser." with a Cancel button, and closing the dialog cancels the sign-in.

Serverpod (v4.0.3) reports a cancelled browser round trip as an unknown error, so the gateway knows a cancel by having asked for it. A cancel on GitHub's own page, or leaving the browser on Android, still reads as a failure; AGENTS.md says so.

The regression test drives the package's front through a change of focus. With the package's behaviour it fails with the same refused connection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>
This commit is contained in:
Tizian 「ティツィアーン」 2026-09-30 20:18:18 +02:00
commit 4ab78d5547
Signed by: raisondetredev
GPG key ID: 07F6FCF405488B64
1 changed files with 703 additions and 8 deletions
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AGENTS.md
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@ -111,6 +111,7 @@ A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS s
- **GitHub keeps only the numeric GitHub ID**: our own slim login (`lib/src/auth/github.dart`) on Serverpod's GitHub helpers; Serverpod's stock GitHub login endpoint, which stores name, email and avatar, is never exposed. GitHub sign-in is on only where the passwords hold `githubClientId` and `githubClientSecret` (in production `GITHUB_CLIENT_ID`/`GITHUB_CLIENT_SECRET` in `deploy/.env`); the app asks `instance.info()`.
- **Linking keeps the person** (`GitHubUpgradeEndpoint`, `requireLogin`): the GitHub ID joins the signed-in anonymous person, who becomes identified and loses the anonymous identity, in one transaction. **Signing in** (`GitHubSignInEndpoint`) only reaches people who have a GitHub account already, and only without a session: Serverpod refuses to issue another person's session inside a signed-in call. Refusals are `GitHubSignInRefusedException` with a reason.
- **Switching devices' person** (the app's `switchToGitHub`): swap the session directly, never through "signed out" (which would start another anonymous account), then end the anonymous session left behind.
- **On Linux and Windows the browser half is the app's own** (`LoopbackWebAuth`, `feature/auth/data/`): the system browser and a loopback address (RFC 8252), put in place of flutter_web_auth_2's own implementation (checked with v5.1.0) before each sign-in. The package's front ends every pending sign-in when the app is resumed, and on the desktop the window regaining focus resumes it, so its loopback server closed before GitHub answered. Ours waits for GitHub, the dialog's Cancel (shown only there), or 5 minutes; the regression test drives the package's front through a focus change. Remove it once the package stops ending sign-ins on focus there. Serverpod (v4.0.3) reports every cancelled browser round trip as an unknown error, so the gateway knows a cancel only by having asked for it; a cancel on GitHub's own page, or leaving the browser on Android, still shows "Couldn't sign in with GitHub."
- **Authorization lives in endpoint code**; Serverpod has no row-level security. Load content filtered by the session's `authUserId`, never by an owner ID the client sends. A row another person owns must be indistinguishable from a missing one. Features involving other people require the `identified` scope, declared via `requiredScopes`, never checked ad hoc.
- **The reference is `DevicesEndpoint`** (`halkyon_learn_server/lib/src/auth/`) with its tests: the owner check sits in the same query (`WHERE "id" = $1 AND "authUserId" = $2`), zero rows means `NotFoundException` (shared, `lib/src/common/`), and every rule has a test that asserts the refusal. Each query carries its SQL as a comment.
- **Serverpod's own helpers aren't guarded**: `ServerSideSessions.revokeSession` deletes by id alone, and `listSessions` without `authUserId` returns everyone's sessions. Never pass them anything a client sent.