feat(auth) : protect admin login with turnstile

lib/auth/server.ts

@@ -3,7 +3,7 @@ import "server-only";
 import { betterAuth } from "better-auth";
 import { drizzleAdapter } from "better-auth/adapters/drizzle";
 import { nextCookies } from "better-auth/next-js";
-import { admin } from "better-auth/plugins";
+import { admin, captcha } from "better-auth/plugins";
 import { headers } from "next/headers";
 
 import { getDb } from "@/db";
@@ -60,7 +60,15 @@ function createAuth() {
         },
       },
     },
-    plugins: [admin({ defaultRole: "admin" }), nextCookies()],
+    plugins: [
+      captcha({
+        provider: "cloudflare-turnstile",
+        secretKey: required("TURNSTILE_SECRET_KEY"),
+        endpoints: ["/sign-in/email"],
+      }),
+      admin({ defaultRole: "admin" }),
+      nextCookies(),
+    ],
   });
 }