examples: add tanstack start with better auth example

examples/react/start-basic-better-auth/.env.example

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+# Better Auth Configuration
+BETTER_AUTH_SECRET=your-secret-key-here-min-32-chars-long
+
+# Better Auth URL (base URL, no /api/auth suffix)
+BETTER_AUTH_URL=http://localhost:10000
+
+# GitHub OAuth Configuration (https://github.com/settings/developers)
+GITHUB_CLIENT_ID=your-github-client-id
+GITHUB_CLIENT_SECRET=your-github-client-secret

examples/react/start-basic-better-auth/.gitignore

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+node_modules
+dist
+.env
+*.local
+.DS_Store
+.tanstack

examples/react/start-basic-better-auth/README.md

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+# TanStack Start - Better Auth Example
+
+A TanStack Start example demonstrating authentication with Better Auth.
+
+- [TanStack Router Docs](https://tanstack.com/router)
+- [Better Auth Documentation](https://www.better-auth.com/)
+
+## Start a new project based on this example
+
+To start a new project based on this example, run:
+
+```sh
+npx gitpick TanStack/router/tree/main/examples/react/start-basic-better-auth start-basic-better-auth
+```
+
+## Setup
+
+This example requires environment variables for Better Auth configuration. Copy the `.env.example` file to `.env` and fill in your GitHub OAuth credentials:
+
+```sh
+cp .env.example .env
+```
+
+### GitHub OAuth Setup
+
+1. Go to [GitHub Developer Settings](https://github.com/settings/developers)
+2. Click "New OAuth App"
+3. Fill in:
+   - Application name: Your app name
+   - Homepage URL: `http://localhost:10000`
+   - Authorization callback URL: `http://localhost:10000/api/auth/callback/github`
+4. Copy the Client ID and Client Secret to your `.env` file
+
+## Getting Started
+
+From your terminal:
+
+```sh
+pnpm install
+pnpm dev
+```
+
+This starts your app in development mode, rebuilding assets on file changes.
+
+## Build
+
+To build the app for production:
+
+```sh
+pnpm build
+```
+
+## Authentication Configuration
+
+This example demonstrates how to integrate Better Auth with TanStack Start. Check the source code for examples of:
+
+- Configuring social authentication providers
+- Protecting routes with authentication
+- Accessing session data in server functions
+
+### Key Files
+
+- `src/utils/auth.ts` - Better Auth server configuration
+- `src/utils/auth-client.ts` - Better Auth client setup
+- `src/routes/__root.tsx` - Session fetching and navigation
+- `src/routes/protected.tsx` - Example of a protected route

examples/react/start-basic-better-auth/package.json

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+{
+  "name": "tanstack-start-example-basic-better-auth",
+  "private": true,
+  "sideEffects": false,
+  "type": "module",
+  "scripts": {
+    "dev": "vite dev",
+    "build": "vite build",
+    "preview": "vite preview",
+    "start": "pnpx srvx --prod -s ../client dist/server/server.js"
+  },
+  "dependencies": {
+    "@tanstack/react-router": "^1.147.0",
+    "@tanstack/react-router-devtools": "^1.147.0",
+    "@tanstack/react-start": "^1.147.0",
+    "better-auth": "^1.4.10",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0",
+    "tailwind-merge": "^2.6.0"
+  },
+  "devDependencies": {
+    "@tailwindcss/vite": "^4.1.18",
+    "@types/node": "^22.5.4",
+    "@types/react": "^19.0.8",
+    "@types/react-dom": "^19.0.3",
+    "@vitejs/plugin-react": "^4.6.0",
+    "tailwindcss": "^4.1.18",
+    "typescript": "^5.7.2",
+    "vite": "^7.1.7",
+    "vite-tsconfig-paths": "^5.1.4"
+  }
+}

examples/react/start-basic-better-auth/src/components/DefaultCatchBoundary.tsx

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+import {
+  ErrorComponent,
+  Link,
+  rootRouteId,
+  useMatch,
+  useRouter,
+} from "@tanstack/react-router";
+import type { ErrorComponentProps } from "@tanstack/react-router";
+
+export function DefaultCatchBoundary({ error }: ErrorComponentProps) {
+  const router = useRouter();
+  const isRoot = useMatch({
+    strict: false,
+    select: (state) => state.id === rootRouteId,
+  });
+
+  console.error("DefaultCatchBoundary Error:", error);
+
+  return (
+    <div className="min-w-0 flex-1 p-4 flex flex-col items-center justify-center gap-6">
+      <ErrorComponent error={error} />
+      <div className="flex gap-2 items-center flex-wrap">
+        <button
+          onClick={() => {
+            router.invalidate();
+          }}
+          className={`px-2 py-1 bg-gray-600 dark:bg-gray-700 rounded-sm text-white uppercase font-extrabold`}
+        >
+          Try Again
+        </button>
+        {isRoot ? (
+          <Link
+            to="/"
+            className={`px-2 py-1 bg-gray-600 dark:bg-gray-700 rounded-sm text-white uppercase font-extrabold`}
+          >
+            Home
+          </Link>
+        ) : (
+          <Link
+            to="/"
+            className={`px-2 py-1 bg-gray-600 dark:bg-gray-700 rounded-sm text-white uppercase font-extrabold`}
+            onClick={(e) => {
+              e.preventDefault();
+              window.history.back();
+            }}
+          >
+            Go Back
+          </Link>
+        )}
+      </div>
+    </div>
+  );
+}

examples/react/start-basic-better-auth/src/components/NotFound.tsx

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+import { Link } from "@tanstack/react-router";
+
+export function NotFound({ children }: { children?: any }) {
+  return (
+    <div className="space-y-2 p-2">
+      <div className="text-gray-600 dark:text-gray-400">
+        {children || <p>The page you are looking for does not exist.</p>}
+      </div>
+      <p className="flex items-center gap-2 flex-wrap">
+        <button
+          onClick={() => window.history.back()}
+          className="bg-emerald-500 text-white px-2 py-1 rounded-sm uppercase font-black text-sm"
+        >
+          Go back
+        </button>
+        <Link
+          to="/"
+          className="bg-cyan-600 text-white px-2 py-1 rounded-sm uppercase font-black text-sm"
+        >
+          Start Over
+        </Link>
+      </p>
+    </div>
+  );
+}

examples/react/start-basic-better-auth/src/routeTree.gen.ts

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+/* eslint-disable */
+
+// @ts-nocheck
+
+// noinspection JSUnusedGlobalSymbols
+
+// This file was automatically generated by TanStack Router.
+// You should NOT make any changes in this file as it will be overwritten.
+// Additionally, you should also exclude this file from your linter and/or formatter to prevent it from being checked or modified.
+
+import { Route as rootRouteImport } from './routes/__root'
+import { Route as ProtectedRouteImport } from './routes/protected'
+import { Route as LoginRouteImport } from './routes/login'
+import { Route as IndexRouteImport } from './routes/index'
+import { Route as ApiAuthSplatRouteImport } from './routes/api/auth/$'
+
+const ProtectedRoute = ProtectedRouteImport.update({
+  id: '/protected',
+  path: '/protected',
+  getParentRoute: () => rootRouteImport,
+} as any)
+const LoginRoute = LoginRouteImport.update({
+  id: '/login',
+  path: '/login',
+  getParentRoute: () => rootRouteImport,
+} as any)
+const IndexRoute = IndexRouteImport.update({
+  id: '/',
+  path: '/',
+  getParentRoute: () => rootRouteImport,
+} as any)
+const ApiAuthSplatRoute = ApiAuthSplatRouteImport.update({
+  id: '/api/auth/$',
+  path: '/api/auth/$',
+  getParentRoute: () => rootRouteImport,
+} as any)
+
+export interface FileRoutesByFullPath {
+  '/': typeof IndexRoute
+  '/login': typeof LoginRoute
+  '/protected': typeof ProtectedRoute
+  '/api/auth/$': typeof ApiAuthSplatRoute
+}
+export interface FileRoutesByTo {
+  '/': typeof IndexRoute
+  '/login': typeof LoginRoute
+  '/protected': typeof ProtectedRoute
+  '/api/auth/$': typeof ApiAuthSplatRoute
+}
+export interface FileRoutesById {
+  __root__: typeof rootRouteImport
+  '/': typeof IndexRoute
+  '/login': typeof LoginRoute
+  '/protected': typeof ProtectedRoute
+  '/api/auth/$': typeof ApiAuthSplatRoute
+}
+export interface FileRouteTypes {
+  fileRoutesByFullPath: FileRoutesByFullPath
+  fullPaths: '/' | '/login' | '/protected' | '/api/auth/$'
+  fileRoutesByTo: FileRoutesByTo
+  to: '/' | '/login' | '/protected' | '/api/auth/$'
+  id: '__root__' | '/' | '/login' | '/protected' | '/api/auth/$'
+  fileRoutesById: FileRoutesById
+}
+export interface RootRouteChildren {
+  IndexRoute: typeof IndexRoute
+  LoginRoute: typeof LoginRoute
+  ProtectedRoute: typeof ProtectedRoute
+  ApiAuthSplatRoute: typeof ApiAuthSplatRoute
+}
+
+declare module '@tanstack/react-router' {
+  interface FileRoutesByPath {
+    '/protected': {
+      id: '/protected'
+      path: '/protected'
+      fullPath: '/protected'
+      preLoaderRoute: typeof ProtectedRouteImport
+      parentRoute: typeof rootRouteImport
+    }
+    '/login': {
+      id: '/login'
+      path: '/login'
+      fullPath: '/login'
+      preLoaderRoute: typeof LoginRouteImport
+      parentRoute: typeof rootRouteImport
+    }
+    '/': {
+      id: '/'
+      path: '/'
+      fullPath: '/'
+      preLoaderRoute: typeof IndexRouteImport
+      parentRoute: typeof rootRouteImport
+    }
+    '/api/auth/$': {
+      id: '/api/auth/$'
+      path: '/api/auth/$'
+      fullPath: '/api/auth/$'
+      preLoaderRoute: typeof ApiAuthSplatRouteImport
+      parentRoute: typeof rootRouteImport
+    }
+  }
+}
+
+const rootRouteChildren: RootRouteChildren = {
+  IndexRoute: IndexRoute,
+  LoginRoute: LoginRoute,
+  ProtectedRoute: ProtectedRoute,
+  ApiAuthSplatRoute: ApiAuthSplatRoute,
+}
+export const routeTree = rootRouteImport
+  ._addFileChildren(rootRouteChildren)
+  ._addFileTypes<FileRouteTypes>()
+
+import type { getRouter } from './router.tsx'
+import type { createStart } from '@tanstack/react-start'
+declare module '@tanstack/react-start' {
+  interface Register {
+    ssr: true
+    router: Awaited<ReturnType<typeof getRouter>>
+  }
+}

examples/react/start-basic-better-auth/src/router.tsx

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+import { createRouter } from "@tanstack/react-router";
+import { routeTree } from "./routeTree.gen";
+import { DefaultCatchBoundary } from "./components/DefaultCatchBoundary";
+import { NotFound } from "./components/NotFound";
+import type { RouterContext } from "./routes/__root";
+
+export function getRouter() {
+  const router = createRouter({
+    routeTree,
+    defaultPreload: "intent",
+    defaultErrorComponent: DefaultCatchBoundary,
+    defaultNotFoundComponent: () => <NotFound />,
+    scrollRestoration: true,
+    context: {
+      session: null,
+    } satisfies RouterContext,
+  });
+  return router;
+}