feat: oauth autoredirect support

[joshtgl]

Description

Adds optional automatic redirect from the sign-in page to the first configured OAuth provider when OAUTH_AUTO_REDIRECT=true.

Let me know if any other changes/updates are needed.

Demo

No UI screenshots included. Behavior change is:

• With OAUTH_AUTO_REDIRECT=true and at least one OAuth provider configured, visiting the sign-in page redirects immediately to the first configured OAuth provider.

Checklist

• I have read CONTRIBUTING.md in its entirety
• I have performed a self-review of my own code
• I have added unit tests to cover my changes
• The last commit successfully passed pre-commit checks
• Any AI code was thoroughly reviewed by me

Summary by CodeRabbit

• New Features

  • Added an optional setting to automatically redirect sign-in when exactly one OAuth provider is configured.
  • Automatic redirection remains disabled by default and is skipped while verification or provider loading is active.
  • Sign-in failures during automatic redirection are reported with a notification.

• Documentation

  • Documented the automatic redirection setting and its configuration requirements.

• Bug Fixes

  • Added validation and warnings for unsupported automatic redirection configurations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 7c6c0cd6-4b42-412a-af7a-80f8d00f855f

📥 Commits

Reviewing files that changed from the base of the PR and between 7ac60d6 and b8727d5.

📒 Files selected for processing (5)

• .env.example
• docs/CONFIGURATION.md
• src/env.ts
• src/pages/auth/signin.tsx
• src/server/auth.ts

🚧 Files skipped from review as they are similar to previous changes (5)

• .env.example
• src/env.ts
• src/pages/auth/signin.tsx
• src/server/auth.ts
• docs/CONFIGURATION.md

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📝 Walkthrough

Walkthrough

Adds the OAUTH_AUTO_REDIRECT setting. The server parses and validates the setting, then passes it to the sign-in page. The page starts OAuth sign-in when exactly one OAuth provider is configured.

Changes

OAuth automatic redirect

Layer / File(s)	Summary
Configuration and provider validation .env.example, docs/CONFIGURATION.md, src/env.ts, src/server/auth.ts	Defines and documents OAUTH_AUTO_REDIRECT, parses it as false by default, and warns when its provider requirements are not met.
Sign-in redirect flow src/pages/auth/signin.tsx	Passes the setting to the sign-in page and calls signIn when exactly one OAuth provider is available, except when sign-in errors, verification, or provider loading prevent the redirect.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Environment
  participant getServerSideProps
  participant Home
  participant OAuthProvider
  Environment->>getServerSideProps: Read env.OAUTH_AUTO_REDIRECT
  getServerSideProps->>Home: Pass oauthAutoRedirect
  Home->>OAuthProvider: Call signIn(provider.id) when one OAuth provider is available

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Possibly related PRs

• oss-apps/split-pro#717: Both PRs define boolean environment variables with false defaults and JSON-based runtime parsing.

Suggested reviewers: krokosik

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: support for OAuth automatic redirection.
Description check	✅ Passed	The description explains the behavior, includes the demo and checklist sections, and records that unit tests were not added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 2

🧹 Nitpick comments (1)

src/env.ts (1)

74-74: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Declare the default in the Zod schema.

OAUTH_AUTO_REDIRECT is optional at Line [74], while the sign-in page requires a boolean. Change the schema to z.boolean().default(false) so validation and the inferred env type use the same contract.

Proposed fix

-    OAUTH_AUTO_REDIRECT: z.boolean().optional(),
+    OAUTH_AUTO_REDIRECT: z.boolean().default(false),

Verify the inferred type with @t3-oss/env-nextjs 0.13.8 after this change. As per coding guidelines, src/env.ts must define fallback defaults with Zod .default().

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/env.ts` at line 74, Update the OAUTH_AUTO_REDIRECT schema entry in the
env validation definition to use z.boolean().default(false) instead of
optional(), so validation and the inferred env type always provide a boolean
while following the project’s Zod default convention.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/pages/auth/signin.tsx`:
- Around line 114-124: Update the automatic redirect logic in the sign-in
useEffect by requiring !error in shouldAutoRedirect, and include error in the
effect dependency list so callback failures do not restart OAuth.
- Around line 114-124: Update the automatic sign-in flow in the useEffect
callback to catch rejected signIn promises and display
toast.error(t('errors.signin_error')). Include t in the effect dependency array
while preserving the existing redirect conditions.

---

Nitpick comments:
In `@src/env.ts`:
- Line 74: Update the OAUTH_AUTO_REDIRECT schema entry in the env validation
definition to use z.boolean().default(false) instead of optional(), so
validation and the inferred env type always provide a boolean while following
the project’s Zod default convention.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 63c833ed-6fb3-4619-929e-1c4c71d5424d

📥 Commits

Reviewing files that changed from the base of the PR and between f0ca6d9 and 60daa81.

📒 Files selected for processing (5)

• .env.example
• docs/CONFIGURATION.md
• src/env.ts
• src/pages/auth/signin.tsx
• src/server/auth.ts

[joshtgl]

I verified auto redirect on my local instance when the setting is enabled/disabled.

[krokosik]

Great, thank you!

[krokosik]

Ready to merge once the conflict is resolved @joshtgl

[joshtgl]

It should be rebased and conflicts resolved.