migrate auth from next-auth to better-auth with magic link support

Replace next-auth with better-auth, adding magic link email login as
the primary auth method and GitHub OAuth as an optional social provider.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

components/auth.tsx

@@ -1,21 +1,42 @@
-import { useEffect } from 'react'
-
-import { useSession, signIn } from 'next-auth/react'
+import { useState } from 'react'
+import { useSession, signIn } from '../lib/auth-client'
+import Input from './input'
+import Button from './button'
 
 export default function Auth({ children }) {
-  const { data: session, status } = useSession()
+  const { data: session, isPending } = useSession()
   const isUser = !!session?.user
+  const [email, setEmail] = useState('')
+  const [loading, setLoading] = useState(false)
+  const [sent, setSent] = useState(false)
+  const [error, setError] = useState('')
 
-  useEffect(() => {
-    if (status === 'loading') return // Do nothing while loading
-    if (!isUser) signIn() // If not authenticated, force log in
-  }, [isUser, status])
+  if (isPending) return <div>Loading...</div>
 
-  if (isUser) {
-    return children
+  if (isUser) return children
+
+  if (process.env.NEXT_PUBLIC_GITHUB_ENABLED) {
+    signIn.social({ provider: "github", callbackURL: window.location.href })
+    return <div>Loading...</div>
   }
 
-  // Session is being fetched, or no user.
-  // If no user, useEffect() will redirect.
-  return <div>Loading...</div>
+  if (sent) return <div>E-Mail verschickt — bitte prüfe dein Postfach.</div>
+
+  async function handleSubmit(e: React.FormEvent) {
+    e.preventDefault()
+    setLoading(true)
+    setError('')
+    const result = await signIn.magicLink({ email, callbackURL: window.location.href })
+    if (result.error) setError(result.error.message)
+    else setSent(true)
+    setLoading(false)
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="max-w-sm mx-auto mt-16">
+      <Input label="E-Mail" name="email" type="email" value={email} onChange={e => setEmail(e.target.value)} required />
+      {error && <p className="text-red-500 text-sm mb-3">{error}</p>}
+      <Button type="submit" loading={loading}>Magic Link senden</Button>
+    </form>
+  )
 }

components/denied.tsx

@@ -1,4 +1,4 @@
-import { signIn } from 'next-auth/react'
+import { signIn } from '../lib/auth-client'
 
 export default function Denied() {
   return (
@@ -8,7 +8,12 @@ export default function Denied() {
         <a
           onClick={(e) => {
             e.preventDefault()
-            signIn()
+            if (process.env.NEXT_PUBLIC_GITHUB_ENABLED) {
+              signIn.social({
+                provider: "github",
+                callbackURL: window.location.href,
+              })
+            }
           }}
         >
           Melde dich an um diese Seite zu sehen.

components/user.tsx

@@ -1,10 +1,10 @@
-import { useSession, signOut } from 'next-auth/react'
+import { useSession, signOut } from '../lib/auth-client'
 import Link from 'next/link'
 
 export default function User() {
-  const { data, status } = useSession()
+  const { data: session, isPending } = useSession()
 
-  if (status === 'loading' || !data?.user?.email) {
+  if (isPending || !session?.user?.email) {
     return null
   }
 
@@ -17,7 +17,7 @@ export default function User() {
         Admin
       </Link>
       <div className="font-extrabold bg-red-400 px-2 py-1 mr-3 rounded-xs">
-        {data.user.email}
+        {session.user.email}
       </div>
       <button onClick={() => signOut()} className="btn btn-blue">
         Logout

helpers/url.ts

@@ -10,4 +10,4 @@ if (process.env.SITE_URL) {
 
 export function getBaseURL(): string {
   return URL
-}
+}

helpers/withAuth.tsx

@@ -1,17 +1,14 @@
-import { SessionProvider } from 'next-auth/react'
 import Auth from '../components/auth'
 
 // This is the HOC
 function withAuth(WrappedComponent: React.FunctionComponent) {
   // Return a new component
-  function withAuth({ session, ...pageProps }) {
+  function withAuth(pageProps) {
     // Render the WrappedComponent with additional props
     return (
-      <SessionProvider session={session}>
-        <Auth>
-          <WrappedComponent {...pageProps} />
-        </Auth>
-      </SessionProvider>
+      <Auth>
+        <WrappedComponent {...pageProps} />
+      </Auth>
     )
   }
 

lib/auth-client.ts

@@ -0,0 +1,8 @@
+import { createAuthClient } from "better-auth/react"
+import { magicLinkClient } from "better-auth/client/plugins"
+
+export const authClient = createAuthClient({
+  plugins: [magicLinkClient()],
+})
+
+export const { signIn, signOut, signUp, useSession } = authClient

lib/auth.ts

@@ -0,0 +1,92 @@
+import { betterAuth } from "better-auth"
+import { magicLink } from "better-auth/plugins"
+import { mongodbAdapter } from "better-auth/adapters/mongodb"
+import { MongoClient, ServerApiVersion } from "mongodb"
+import { MONGO_URI } from "../db"
+import nodemailer from "nodemailer"
+
+async function sendEmail({ to, subject, url }: { to: string; subject: string; url: string }) {
+  const transporter = nodemailer.createTransport({
+    host: "wirtanen.uberspace.de",
+    port: 465,
+    secure: true,
+    auth: {
+      user: process.env.SMTP_USER,
+      pass: process.env.SMTP_PASS,
+    },
+  })
+  await transporter.sendMail({
+    from: process.env.FROM_EMAIL,
+    to,
+    subject,
+    text: url,
+    html: `<p>Click <a href="${url}">here</a> to sign in.</p>`,
+  })
+}
+
+const ADMIN_EMAIL = process.env.ADMIN_EMAIL
+const GITHUB_USERS_GRANTED = ['111471']
+const GITHUB_CLIENT_ID = process.env.GITHUB_CLIENT_ID;
+const GITHUB_CLIENT_SECRET = process.env.GITHUB_CLIENT_SECRET;
+const GITHUB_ENABLED = Boolean(GITHUB_CLIENT_SECRET?.length && GITHUB_CLIENT_ID?.length);
+
+const client = new MongoClient(MONGO_URI, {
+  serverApi: {
+    version: ServerApiVersion.v1,
+    strict: true,
+    deprecationErrors: true,
+  }
+})
+
+export const auth = betterAuth({
+  database: mongodbAdapter(client.db()),
+  plugins: [
+    magicLink({
+      sendMagicLink: async ({ email, url }) => {
+        await sendEmail({ to: email, subject: "Sign in to Pfadi Bussle", url })
+      },
+    }),
+  ],
+  ...(GITHUB_ENABLED ? {
+    socialProviders: {
+      github: {
+        provider: 'github',
+        clientId: GITHUB_CLIENT_ID,
+        clientSecret: GITHUB_CLIENT_SECRET,
+      },
+    },
+  } : {}),
+  account: {
+    accountLinking: {
+      enabled: true,
+      trustedProviders: ["github"],
+    },
+  },
+  user: {
+    additionalFields: {
+      role: {
+        type: "string",
+        defaultValue: "user",
+      },
+    },
+  },
+  onRequest: async (request) => {
+    // Authorization logic
+    const session = request.context?.session
+    if (session?.user) {
+      const account = request.context?.account
+
+      // GitHub provider check
+      if (account?.providerId === 'github') {
+        if (!GITHUB_USERS_GRANTED.includes(account.providerAccountId)) {
+          throw new Error('Unauthorized GitHub user')
+        }
+      }
+
+      // Email check - only allow admin email
+      if (session.user.email && session.user.email !== ADMIN_EMAIL) {
+        throw new Error('Unauthorized email')
+      }
+    }
+  },
+})

package.json

@@ -14,19 +14,19 @@
     "@date-fns/tz": "^1.2.0",
     "@mdx-js/loader": "^3.1.1",
     "@mdx-js/react": "^3.1.1",
-    "@next-auth/mongodb-adapter": "^1.1.3",
     "@next/mdx": "^16.1.6",
     "@types/mdx": "^2.0.11",
     "@types/nodemailer": "^7.0.9",
     "@vercel/analytics": "^1.6.1",
     "autoprefixer": "^10.4.24",
+    "better-auth": "^1.4.18",
     "classnames": "^2.5.1",
     "date-fns": "^4.1.0",
     "googleapis": "^171.4.0",
     "ics": "^3.8.1",
+    "mongodb": "^7.1.0",
     "mongoose": "^9.2.1",
     "next": "^16.1.6",
-    "next-auth": "^4.24.13",
     "next-axiom": "^1.10.0",
     "nodemailer": "^8.0.1",
     "react": "^19.2.4",
@@ -53,4 +53,4 @@
       "^.+\\.(ts|tsx)$": "ts-jest"
     }
   }
-}
+}

pages/api/auth/[...all].ts

@@ -0,0 +1,37 @@
+import { auth } from "../../../lib/auth"
+import type { NextApiRequest, NextApiResponse } from "next"
+
+export const config = {
+  api: {
+    bodyParser: false,
+  },
+}
+
+export default async function handler(req: NextApiRequest, res: NextApiResponse) {
+  const baseUrl = process.env.BETTER_AUTH_URL || "http://localhost:3000"
+  const url = new URL(req.url!, baseUrl)
+
+  let body: Buffer | undefined
+  if (req.method !== "GET" && req.method !== "HEAD") {
+    body = await new Promise<Buffer>((resolve, reject) => {
+      const chunks: Buffer[] = []
+      req.on("data", (chunk: Buffer) => chunks.push(chunk))
+      req.on("end", () => resolve(Buffer.concat(chunks)))
+      req.on("error", reject)
+    })
+  }
+
+  const webRequest = new Request(url.toString(), {
+    method: req.method,
+    headers: req.headers as HeadersInit,
+    body: body,
+  })
+
+  const response = await auth.handler(webRequest)
+
+  res.status(response.status)
+  response.headers.forEach((value, key) => {
+    res.setHeader(key, value)
+  })
+  res.end(await response.text())
+}

pages/api/auth/[...nextauth].ts

@@ -1,73 +0,0 @@
-import { NextApiRequest, NextApiResponse } from 'next'
-import NextAuth from 'next-auth'
-import EmailProvider from 'next-auth/providers/email'
-import GitHubProvider from 'next-auth/providers/github'
-
-import { MongoDBAdapter } from '@next-auth/mongodb-adapter'
-import { MONGO_URI } from '../../../db'
-import { MongoClient, ServerApiVersion } from 'mongodb'
-
-let client: MongoClient
-
-const ADMIN_EMAIL = process.env.ADMIN_EMAIL
-const GITHUB_USERS_GRANTED = ['111471']
-
-async function getMongoClient() {
-  if (!client) {
-    client = new MongoClient(MONGO_URI, {
-      serverApi: {
-        version: ServerApiVersion.v1,
-        strict: true,
-        deprecationErrors: true,
-      }
-    })
-    await client.connect()
-  }
-
-  return client
-}
-
-export default async function auth(req: NextApiRequest, res: NextApiResponse) {
-  return await NextAuth(req, res, {
-    secret: process.env.NEXTAUTH_SECRET,
-    adapter: MongoDBAdapter(getMongoClient()),
-    providers: [
-      GitHubProvider({
-        clientId: process.env.GITHUB_CLIENT_ID,
-        clientSecret: process.env.GITHUB_CLIENT_SECRET,
-      }),
-      EmailProvider({
-        server: {
-          host: "wirtanen.uberspace.de",
-          port: 465,
-          secure: true,
-          auth: {
-            user: process.env.SMTP_USER,
-            pass: process.env.SMTP_PASS,
-          },
-          logger: true,
-          debug: true,
-        },
-        from: process.env.FROM_EMAIL,
-      }),
-    ],
-    callbacks: {
-      async signIn({ account, email }) {
-        // if user sigin requested magic link via EmailProvider
-        if (account.provider === 'email') {
-          if (email?.verificationRequest) {
-            // only allow admins by email entered
-            return account.providerAccountId === ADMIN_EMAIL
-          }
-
-          // if user accesses with magic link, also only allow admin
-          return account.providerAccountId === ADMIN_EMAIL
-        } else if (account.provider === 'github') {
-          // only one and only one user
-          return GITHUB_USERS_GRANTED.includes(account.providerAccountId)
-        }
-        return false
-      },
-    },
-  })
-}