add nextauth_url env var

make sure the oauth callback knows where to go

env.example

@@ -1,6 +1,7 @@
 DISCORD_CLIENT_ID=
 DISCORD_CLIENT_SECRET=
 NEXTAUTH_SECRET=
+NEXTAUTH_URL=
 DISCORD_GUILD_ID=
 DISCORD_REQUIRED_ROLE_ID=
 DISCORD_BOT_TOKEN=

src/app/lib/auth.ts

@@ -39,4 +39,7 @@ export const authOptions: NextAuthOptions = {
     error: "/auth/error",
   },
   secret: process.env.NEXTAUTH_SECRET,
+  ...(process.env.NEXTAUTH_URL && {
+    url: process.env.NEXTAUTH_URL,
+  }),
 };