Router Coreauth And Guards

Core Patterns

Router Context for Auth State

Auth state flows into the router via createRootRouteWithContext and RouterProvider's context prop:

// src/routes/__root.tsx
import { createRootRouteWithContext, Outlet } from '@tanstack/react-router'

interface AuthState {
  isAuthenticated: boolean
  user: { id: string; username: string; email: string } | null
  login: (username: string, password: string) => Promise<void>
  logout: () => void
}

interface MyRouterContext {
  auth: AuthState
}

export const Route = createRootRouteWithContext<MyRouterContext>()({
  component: () => <Outlet />,
})

// src/router.tsx
import { createRouter } from '@tanstack/react-router'
import { routeTree } from './routeTree.gen'

export const router = createRouter({
  routeTree,
  context: {
    auth: undefined!, // placeholder — filled by RouterProvider context prop
  },
})

declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}

// src/App.tsx
import { RouterProvider } from '@tanstack/react-router'
import { AuthProvider, useAuth } from './auth'
import { router } from './router'

function InnerApp() {
  const auth = useAuth()
  // context prop injects live auth state WITHOUT recreating the router
  return <RouterProvider router={router} context={{ auth }} />
}

function App() {
  return (
    <AuthProvider>
      <InnerApp />
    </AuthProvider>
  )
}

The router is created once with a placeholder. RouterProvider's context prop injects the live auth state on each render — this avoids recreating the router on auth changes (which would reset caches and rebuild the route tree).

Redirect-Based Auth with Redirect-Back

Save the current location in search params so you can redirect back after login:

// src/routes/_authenticated.tsx
import { createFileRoute, redirect } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated')({
  beforeLoad: ({ context, location }) => {
    if (!context.auth.isAuthenticated) {
      throw redirect({
        to: '/login',
        search: { redirect: location.href },
      })
    }
  },
})

// src/routes/login.tsx
import { createFileRoute, redirect } from '@tanstack/react-router'
import { useState, type FormEvent } from 'react'

// Validate redirect target to prevent open redirect attacks
function sanitizeRedirect(url: unknown): string {
  if (typeof url !== 'string' || !url.startsWith('/') || url.startsWith('//')) {
    return '/'
  }
  return url
}

export const Route = createFileRoute('/login')({
  validateSearch: (search) => ({
    redirect: sanitizeRedirect(search.redirect),
  }),
  beforeLoad: ({ context, search }) => {
    if (context.auth.isAuthenticated) {
      throw redirect({ to: search.redirect })
    }
  },
  component: LoginComponent,
})

function LoginComponent() {
  const { auth } = Route.useRouteContext()
  const search = Route.useSearch()
  const navigate = Route.useNavigate()
  const [username, setUsername] = useState('')
  const [password, setPassword] = useState('')
  const [error, setError] = useState('')

  const handleSubmit = async (e: FormEvent) => {
    e.preventDefault()
    try {
      await auth.login(username, password)
      navigate({ to: search.redirect })
    } catch {
      setError('Invalid credentials')
    }
  }

  return (
    <form onSubmit={handleSubmit}>
      {error && <div>{error}</div>}
      <input value={username} onChange={(e) => setUsername(e.target.value)} />
      <input
        type="password"
        value={password}
        onChange={(e) => setPassword(e.target.value)}
      />
      <button type="submit">Sign In</button>
    </form>
  )
}

Non-Redirect Auth (Inline Login)

Instead of redirecting, show a login form in place of the Outlet:

// src/routes/_authenticated.tsx
import { createFileRoute, Outlet } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated')({
  component: AuthenticatedLayout,
})

function AuthenticatedLayout() {
  const { auth } = Route.useRouteContext()

  if (!auth.isAuthenticated) {
    return <LoginForm />
  }

  return <Outlet />
}

This keeps the URL unchanged — the user stays on the same page and sees a login form instead of protected content. After authentication, <Outlet /> renders and child routes appear.

RBAC with Roles and Permissions

Extend auth state with role/permission helpers, then check in beforeLoad:

// src/auth.tsx
interface User {
  id: string
  username: string
  email: string
  roles: string[]
  permissions: string[]
}

interface AuthState {
  isAuthenticated: boolean
  user: User | null
  hasRole: (role: string) => boolean
  hasAnyRole: (roles: string[]) => boolean
  hasPermission: (permission: string) => boolean
  hasAnyPermission: (permissions: string[]) => boolean
  login: (username: string, password: string) => Promise<void>
  logout: () => void
}

Admin-only layout route:

// src/routes/_authenticated/_admin.tsx
import { createFileRoute, redirect } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated/_admin')({
  beforeLoad: ({ context, location }) => {
    if (!context.auth.hasRole('admin')) {
      throw redirect({
        to: '/unauthorized',
        search: { redirect: location.href },
      })
    }
  },
})

Multi-role access:

// src/routes/_authenticated/_moderator.tsx
import { createFileRoute, redirect } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated/_moderator')({
  beforeLoad: ({ context, location }) => {
    if (!context.auth.hasAnyRole(['admin', 'moderator'])) {
      throw redirect({
        to: '/unauthorized',
        search: { redirect: location.href },
      })
    }
  },
})

Permission-based:

// src/routes/_authenticated/_users.tsx
import { createFileRoute, redirect } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated/_users')({
  beforeLoad: ({ context, location }) => {
    if (!context.auth.hasAnyPermission(['users:read', 'users:write'])) {
      throw redirect({
        to: '/unauthorized',
        search: { redirect: location.href },
      })
    }
  },
})

Page-level permission check (nested under an already-role-protected layout):

// src/routes/_authenticated/_users/manage.tsx
import { createFileRoute } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated/_users/manage')({
  beforeLoad: ({ context }) => {
    if (!context.auth.hasPermission('users:write')) {
      throw new Error('Write permission required')
    }
  },
  component: UserManagement,
})

function UserManagement() {
  const { auth } = Route.useRouteContext()
  const canDelete = auth.hasPermission('users:delete')

  return (
    <div>
      <h1>User Management</h1>
      {canDelete && <button>Delete User</button>}
    </div>
  )
}

Handling Auth Check Failures (isRedirect)

When beforeLoad has a try/catch, redirects (which work by throwing) can get swallowed. Use isRedirect to re-throw:

import { createFileRoute, redirect, isRedirect } from '@tanstack/react-router'

export const Route = createFileRoute('/_authenticated')({
  beforeLoad: async ({ context, location }) => {
    try {
      const user = await verifySession(context.auth)
      if (!user) {
        throw redirect({
          to: '/login',
          search: { redirect: location.href },
        })
      }
      return { user }
    } catch (error) {
      if (isRedirect(error)) throw error // re-throw redirect, don't swallow it
      // Actual error — redirect to login
      throw redirect({
        to: '/login',
        search: { redirect: location.href },
      })
    }
  },
})

Common Mistakes

HIGH: Auth check in component instead of beforeLoad

Component-level auth checks cause a flash of protected content before the redirect:

// WRONG — protected content renders briefly before redirect
export const Route = createFileRoute('/_authenticated/dashboard')({
  component: () => {
    const auth = useAuth()
    if (!auth.isAuthenticated) return <Navigate to="/login" />
    return <Dashboard />
  },
})

// CORRECT — beforeLoad runs before any rendering
export const Route = createFileRoute('/_authenticated/dashboard')({
  beforeLoad: ({ context }) => {
    if (!context.auth.isAuthenticated) {
      throw redirect({ to: '/login' })
    }
  },
  component: Dashboard,
})

beforeLoad runs before any component rendering and before the loader. It completely prevents the flash.

HIGH: Not re-throwing redirects in try/catch

redirect() works by throwing. If beforeLoad has a try/catch, the redirect gets swallowed:

// WRONG — redirect is caught and swallowed
beforeLoad: async ({ context }) => {
  try {
    await validateSession(context.auth)
  } catch (e) {
    console.error(e) // swallows the redirect!
  }
}

// CORRECT — use isRedirect to distinguish intentional redirects from errors
import { isRedirect } from '@tanstack/react-router'

beforeLoad: async ({ context }) => {
  try {
    await validateSession(context.auth)
  } catch (e) {
    if (isRedirect(e)) throw e
    console.error(e)
  }
}

MEDIUM: Conditionally rendering root route component

The root route always renders regardless of auth state. You cannot conditionally render its component:

// WRONG — root route always renders, this doesn't protect anything
export const Route = createRootRoute({
  component: () => {
    if (!isAuthenticated()) return <Login />
    return <Outlet />
  },
})

// CORRECT — use a pathless layout route for auth boundaries
// src/routes/_authenticated.tsx
export const Route = createFileRoute('/_authenticated')({
  beforeLoad: ({ context }) => {
    if (!context.auth.isAuthenticated) {
      throw redirect({ to: '/login' })
    }
  },
})

Place protected routes as children of the _authenticated layout route. Public routes (login, home, etc.) live outside it.

Cross-References

• See also: router-core/data-loading/SKILL.md — beforeLoad runs before loader; auth context flows into loader via route context