docs: add proxy example (#9077)

* chore: add Preview Deployment example

* simplify package.json

* chore(examples): bump to `next-auth@beta`

apps/proxy/.env.example

@@ -0,0 +1,8 @@
+VERCEL="1"
+# https://vercel.com/changelog/corepack-experimental-is-now-available
+ENABLE_EXPERIMENTAL_COREPACK="1"
+
+# https://authjs.dev/getting-started/deployment#securing-a-preview-deployment
+AUTH_SECRET= # openssl rand -base64 64
+AUTH_GITHUB_ID=
+AUTH_GITHUB_SECRET=

apps/proxy/.gitignore

@@ -0,0 +1,15 @@
+# dependencies
+/node_modules
+
+# misc
+.DS_Store
+*.pem
+
+# local env files
+.env*.local
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo

apps/proxy/README.md

@@ -0,0 +1 @@
+TODO

apps/proxy/api/[auth].ts

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+import { Auth, AuthConfig } from "@auth/core"
+import GitHub from "@auth/core/providers/github"
+
+export default function handler(req: Request) {
+  return Auth(req, getDefaults({ providers: [GitHub] }))
+}
+
+export const config = { runtime: "edge" }
+
+export function getDefaults(config: AuthConfig) {
+  config.secret ??= process.env.AUTH_SECRET
+  config.trustHost ??= !!process.env.VERCEL
+  config.redirectProxyUrl ??= process.env.AUTH_REDIRECT_PROXY_URL
+  config.providers = config.providers.map((p) => {
+    const finalProvider = typeof p === "function" ? p() : p
+    if (finalProvider.type === "oauth" || finalProvider.type === "oidc") {
+      const ID = finalProvider.id.toUpperCase()
+      finalProvider.clientId ??= process.env[`AUTH_${ID}_ID`]
+      finalProvider.clientSecret ??= process.env[`AUTH_${ID}_SECRET`]
+      if (finalProvider.type === "oidc") {
+        finalProvider.issuer ??= process.env[`AUTH_${ID}_ISSUER`]
+      }
+    }
+    return finalProvider
+  })
+  return config
+}

apps/proxy/api/callback/[auth].ts

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+export { default } from "../[auth].js"
+export const config = { runtime: "edge" }

apps/proxy/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "proxy",
+  "description": "Proxy for Auth.js hosted examples",
+  "private": true,
+  "type": "module",
+  "dependencies": {
+    "@auth/core": "latest"
+  }
+}

apps/proxy/tsconfig.json

@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "preserve",
+    "incremental": true,
+    "skipLibCheck": true
+  },
+  "include": [
+    "**/*.ts",
+  ],
+  "exclude": [
+    "node_modules",
+  ]
+}