[Docs fix] Added missing baseUrl property in the auth.ts template

[DaveVaval]

• The expo framework guide was missing an important property, baseUrl, from the auth.ts template file. For people who are new to convex and better auth it may not be obvious as to what goes in there, and I personally fell into that trap.

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Summary by CodeRabbit

• Documentation
  • Updated Expo framework guide with improved Better Auth configuration, including proper setup of site URL from environment variables and trusted origins for enhanced security.

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[coderabbitai]

Walkthrough

Documentation for the Expo framework guide is updated to retrieve the site URL from the CONVEX_SITE_URL environment variable and configure it as the base URL for the Better Auth instance while extending trusted origins.

Changes

Cohort / File(s)	Summary
Expo Configuration Update docs/content/docs/framework-guides/expo.mdx	Adds environment-based site URL retrieval; stores CONVEX_SITE_URL in internal constant; passes baseUrl: siteUrl to Better Auth instance and extends trustedOrigins to include the site URL.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

• Simple documentation update with configuration pattern changes
• No logic changes or public API modifications
• Straightforward environment variable integration

Poem

🐰 A rabbit hops through docs with glee,
Environment whispers: "Take me, see?"
Config flows smooth as morning dew,
From CONVEX_SITE_URL, something new!
Trust grows wider, origins align—
This Expo guide? Absolutely mine! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly and concisely describes the main change: adding a missing baseUrl property to the auth.ts template in documentation, which matches the objective of the PR.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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📒 Files selected for processing (1)

• docs/content/docs/framework-guides/expo.mdx (1 hunks)

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🔇 Additional comments (4)

docs/content/docs/framework-guides/expo.mdx (4)

89-90: Clarify environment variable naming in code vs. documentation.

The docs show setting EXPO_PUBLIC_CONVEX_SITE_URL (with the EXPO_PUBLIC_ prefix for Expo's client-side env vars), but the code at line 126 reads process.env.CONVEX_SITE_URL (without the prefix). If both need to be set separately for backend/frontend, this should be documented explicitly. If only one should be used, ensure consistency.

Also applies to: 101-101

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125-126: Address fallback behavior and environment variable requirement.

The fallback to an empty string (process.env.CONVEX_SITE_URL || "") means misconfigured deployments may proceed silently rather than fail early. Consider whether this should:

• Use a non-null assertion (like line 320 does: process.env.SITE_URL!) to catch missing configuration, or
• Include a more explicit error or validation.

Additionally, ensure the environment variable name matches what's documented for users to set.

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320-320: Align environment variable naming with the main Expo section.

The Expo Web support section uses process.env.SITE_URL while the primary Expo section uses process.env.CONVEX_SITE_URL. Ensure the variable names are consistent across both examples, or document why they differ.

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133-133: Good addition of baseUrl and trustedOrigins.

The core fix—adding baseUrl: siteUrl and including siteUrl in trustedOrigins—is correct and addresses the PR's stated goal. Once the environment variable naming and fallback concerns are resolved, this should resolve the missing configuration issue for new users.

Also applies to: 139-139

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[Alvi24]

This causes an error in Nextjs if using betterAuth for both an expo and nextjs projects since
baseURL should be set to the local site url(http://localhost:3000).
Changing the baseURL causes an state_mismatch error