asp.net core 圖片驗證碼，后台驗證

驗證方法：

public static string VerificationCodeCacheFormat="vcode_cache_{0}";

public IActionResult ValidateCode()
        {
            VerificationCodeServices _vierificationCodeServices = new VerificationCodeServices();
            string code = "";
            System.IO.MemoryStream ms = _vierificationCodeServices.Create(out code);
            code = code.ToLower();//驗證碼不分大小寫
            //HttpContext.Session.SetString("SupportValidateCode", code);
            Response.Body.Dispose();
            //ViewBag.code = code;
            var token = Guid.NewGuid().ToString();
            ViewBag.token = token;
            var cacheKey = string.Format(VerificationCodeCacheFormat, token);
            _memoryCache.Set(cacheKey, code, new MemoryCacheEntryOptions()
                    .SetSlidingExpiration(TimeSpan.FromMinutes(20)));
            CookieOptions options = new CookieOptions();
            Response.Cookies.Append("validatecode", token);
            return File(ms.ToArray(), @"image/png");
        }
        /// <summary>
        /// 驗證碼改為后台驗證
        /// </summary>
        /// <param name="userToken"></param>
        /// <param name="userVerCode"></param>
        /// <returns></returns>
        public bool VerifyUserInputCode(string userToken, string userVerCode)
        {
            var cacheKey = string.Format(VerificationCodeCacheFormat, userToken.ToString());
            var vCode = "";
            if (!_memoryCache.TryGetValue(cacheKey, out vCode)) return false;
            if (vCode.ToLower() != userVerCode.ToLower()) return false;
            _memoryCache.Remove(cacheKey);
            return true;
        }

生成驗證碼及其圖片

using System;
using System.Collections.Generic;
using System.DrawingCore;
using System.DrawingCore.Imaging;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
namespace homepage.Classes
{
    ///NuGet中引入第三方 ZKWeb.System.Drawing 3.0版本

    /// <summary>
    /// 圖片驗證碼
    /// </summary>
    public class VerificationCodeServices
    {
        /// <summary>  
        /// 生成指定長度的隨機字符串 
        /// </summary>  
        /// <param name="codeLength">字符串的長度</param>  
        /// <returns>返回隨機數字符串</returns>  
        private string RndomStr(int codeLength)
        {
            //組成字符串的字符集合  0-9數字、大小寫字母
            string chars = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,P,P,Q,R,S,T,U,V,W,X,Y,Z";

            string[] charArray = chars.Split(new Char[] { ',' });   
            string code = ""; 
            int temp = -1;//記錄上次隨機數值，盡量避避免生產幾個一樣的隨機數  
            Random rand = new Random();
            //采用一個簡單的算法以保證生成隨機數的不同  
            for (int i = 1; i < codeLength + 1; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));//初始化隨機類  
                }
                int t = rand.Next(61);
                if (temp == t)
                {
                    return RndomStr(codeLength);//如果獲取的隨機數重復，則遞歸調用  
                }
                temp = t;//把本次產生的隨機數記錄起來  
                code += charArray[t];//隨機數的位數加一  
            }
            return code;
        }

        /// <summary>  
        /// 將生成的字符串寫入圖像文件  
        /// </summary>  
        /// <param name="code">驗證碼字符串</param>
        /// <param name="length">生成位數（默認4位）</param>  

        public MemoryStream Create(out string code, int length = 4)
        {
            code = RndomStr(length);
            Bitmap Img = null;
            Graphics graphics = null;
            MemoryStream ms = null;
            Random random = new Random();
            //顏色集合  
            Color[] color = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
            //字體集合
            string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋體" };
            //定義圖像的大小，生成圖像的實例  
            Img = new Bitmap((int)code.Length * 18, 32);
            graphics = Graphics.FromImage(Img);//從Img對象生成新的Graphics對象    
            graphics.Clear(Color.White);//背景設為白色  

            //在隨機位置畫背景點  

            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(Img.Width);
                int y = random.Next(Img.Height);
                graphics.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }

            //驗證碼繪制在graphics中  

            for (int i = 0; i < code.Length; i++)
            {
                int colorIndex = random.Next(7);//隨機顏色索引值  
                int fontIndex = random.Next(4);//隨機字體索引值  
                Font font = new Font(fonts[fontIndex], 15, FontStyle.Bold);//字體  
                Brush brush = new SolidBrush(color[colorIndex]);//顏色  
                int y = 4;
                if ((i + 1) % 2 == 0)//控制驗證碼不在同一高度  
                {
                    y = 2;
                }
                graphics.DrawString(code.Substring(i, 1), font, brush, 3 + (i * 12), y);//繪制一個驗證字符  
            }
            ms = new MemoryStream();//生成內存流對象  
            Img.Save(ms, ImageFormat.Png);//將此圖像以Png圖像文件的格式保存到流中  
            graphics.Dispose();
            Img.Dispose();
            return ms;
        }
    }
}

 

以上只適用於一個頁面只有一個的驗證碼的情況，下面改進為可以一個頁面多個驗證碼：

ValidateCode方法改為：
     
   public IActionResult ValidateCode(string identify = "")
        {
            VerificationCodeServices _vierificationCodeServices = new VerificationCodeServices();
            string code = "";
            System.IO.MemoryStream ms = _vierificationCodeServices.Create(out code);
            code = code.ToLower();//驗證碼不分大小寫  
            Response.Body.Dispose();
            var token = Guid.NewGuid().ToString();
            ViewBag.token = token;
            var cacheKey = string.Format(VerificationCodeCacheFormat, token);
            _memoryCache.Set(cacheKey, code, new MemoryCacheEntryOptions()
                    .SetSlidingExpiration(TimeSpan.FromMinutes(20)));
            CookieOptions options = new CookieOptions();
            Response.Cookies.Append("validatecode"+ identify, token);
            return File(ms.ToArray(), @"image/png");
        }

當頁面只有一個驗證碼的時候，頁面寫法：

                                                      <p>
                                                            請輸入驗證碼：<br><input type="text" id="validateCode" class="form-control" />
                                                            <img id="imgVerify" src="~/Home/ValidateCode" alt="看不清？點擊更換" onclick="this.src = this.src + '?'" style="vertical-align:middle;" />
                                                        </p>

當頁面多個驗證碼：

                                    <p>
                                            <input name="verification_code" type="text" maxlength="5" id="code_other" class="form-control tbText">
                                            <img id="imgVerifyOther" src="~/Home/ValidateCode?identify=other" alt="看不清？點擊更換" onclick="this.src = 'ValidateCode?identify=other&' + Math.random()" style="vertical-align:middle;" />
                                        </p>