app.module.ts

// ...imports
import { MiddlewareConsumer, Module, NestModule, RequestMethod } from '@nestjs/common';
import { ServeHTMLMiddleware } from './app.middleware';

@Module({
// ...module options
})
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer
      .apply(ServeHTMLMiddleware)
      .forRoutes({ path: '*', method: RequestMethod.GET});
  }
}