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next.config.ts

@@ -1,6 +1,7 @@
 import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
+  basePath: process.env.BASE_PATH,
 	reactStrictMode: true,
 	output: "standalone",
 	images: {

src/app/api/auth/[...nextauth]/route.ts

@@ -1,2 +1,33 @@
+// import { handlers } from "@/auth";
+// export const { GET, POST } = handlers;
+//
+import { NextRequest } from "next/server";
+
 import { handlers } from "@/auth";
-export const { GET, POST } = handlers;
+
+const basePath = process.env.BASE_PATH ?? "";
+
+function rewriteRequest(request: NextRequest) {
+	const { protocol, host, pathname } = request.nextUrl;
+
+	const headers = request.headers;
+	// Host rewrite adopted from next-auth/packages/core/src/lib/utils/env.ts:createActionURL
+	const detectedHost = headers.get("x-forwarded-host") ?? host;
+	const detectedProtocol = headers.get("x-forwarded-proto") ?? protocol;
+	const _protocol = detectedProtocol.endsWith(":")
+		? detectedProtocol
+		: detectedProtocol + ":";
+	const url = new URL(
+		`${_protocol}//${detectedHost}${basePath}${pathname}${request.nextUrl.search}`,
+	);
+
+	return new NextRequest(url, request);
+}
+
+export async function GET(request: NextRequest) {
+	return await handlers.GET(rewriteRequest(request));
+}
+
+export async function POST(request: NextRequest) {
+	return await handlers.POST(rewriteRequest(request));
+}

src/auth.ts

@@ -32,7 +32,10 @@ export const providerMap = providers.map((provider) => {
 	}
 });
 
+const basePath = process.env.BASE_PATH ?? ''
+
 const config = {
+  basePath: `${basePath}/api/auth`,
 	providers,
 	pages: {
 		signIn: "/signin",