add 验证码demo示例

test/WebSites/OAuth2Integration/ResourceServer/Controllers/CaptchaController.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using NCaptcha.Abstractions;
+using NCaptcha.AspNetCore.Extensions;
+
+namespace OAuth2Integration.ResourceServer.Controllers
+{
+    [Route("captcha")]
+    public class CaptchaController : Controller
+    {
+        private readonly ICaptchaGenerator _captchaGenerator;
+
+        public CaptchaController(ICaptchaGenerator captchaGenerator)
+        {
+            _captchaGenerator = captchaGenerator;
+        }
+
+        [Produces("image/gif", Type = typeof(FileContentResult))]
+        [HttpGet]
+        public async Task<IActionResult> OnGetCaptchaAsync() => await _captchaGenerator.GetCaptchaFileResultAsync();
+    }
+}