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doc: add auth middleware example to examples folder #116

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28 changes: 28 additions & 0 deletions example/auth-plugin.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
import { Elysia, t } from 'elysia'
import { jwt } from '../src'

const authPlugin = new Elysia({ name: 'authPlugin' })
.use(
jwt({
name: 'jwt',
secret: 'top-secret',
schema: t.Object({
name: t.String()
})
})
)
.derive(async ({ cookie: { auth }, jwt }) => {
const user = await jwt.verify(auth.value)
if (!user) throw new Error('Unauthorized')
return { user: user }
})
Comment on lines +14 to +18
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@coderabbitai coderabbitai bot Nov 19, 2025

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⚠️ Potential issue | 🔴 Critical

Guard against missing auth cookie to avoid runtime errors

If the auth cookie is absent (unauthenticated request or different cookie name), auth will be undefined and auth.value will throw a TypeError before you can treat the request as unauthorized. That will likely surface as a 500 instead of a clean 401-style auth failure.

Consider defensively checking the cookie before verifying the token:

-	.derive(async ({ cookie: { auth }, jwt }) => {
-		const user = await jwt.verify(auth.value)
-		if (!user) throw new Error('Unauthorized')
-		return { user: user }
-	})
+	.derive(async ({ cookie: { auth }, jwt }) => {
+		const token = auth?.value
+
+		if (!token) {
+			throw new Error('Unauthorized')
+		}
+
+		const user = await jwt.verify(token)
+
+		if (!user) {
+			throw new Error('Unauthorized')
+		}
+
+		return { user }
+	})

This keeps the middleware semantics (all failures become “unauthorized”) while avoiding low-level runtime errors from missing cookies.

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
.derive(async ({ cookie: { auth }, jwt }) => {
const user = await jwt.verify(auth.value)
if (!user) throw new Error('Unauthorized')
return { user: user }
})
.derive(async ({ cookie: { auth }, jwt }) => {
const token = auth?.value
if (!token) {
throw new Error('Unauthorized')
}
const user = await jwt.verify(token)
if (!user) {
throw new Error('Unauthorized')
}
return { user }
})
🤖 Prompt for AI Agents 
In example/auth-plugin.ts around lines 14 to 18, the code assumes cookie.auth
exists and accesses auth.value which can raise a TypeError if the cookie is
missing; update the derive handler to first check that cookie.auth is present
and has a value (e.g., early-throw an Unauthorized error if missing), then call
jwt.verify inside a try/catch (or otherwise handle verification failures) and
throw the same Unauthorized error on any verification or falsy user result so
all failure modes produce a controlled 401-style response instead of a runtime
500.

.as('scoped')

const protectedRoutes = new Elysia()
.use(authPlugin)
.get('/me', ({ user }) => `Viewing protected data as ${user.name}`)

const app = new Elysia()
.use(protectedRoutes)
.get('/public', () => ({ message: 'Public Data' }))
.listen(8080)