feat(server): make captcha modular (#5961)

packages/backend/server/src/plugins/captcha/controller.ts

@@ -0,0 +1,17 @@
+import { Controller, Get } from '@nestjs/common';
+
+import { Public } from '../../core/auth';
+import { Throttle } from '../../fundamentals';
+import { CaptchaService } from './service';
+
+@Throttle('strict')
+@Controller('/api/auth')
+export class CaptchaController {
+  constructor(private readonly captcha: CaptchaService) {}
+
+  @Public()
+  @Get('/challenge')
+  async getChallenge() {
+    return this.captcha.getChallengeToken();
+  }
+}