🎨 #1733 微信支付服务商配置优化，增加服务商合单支付接口

* art:微信服务商配置优化

* new:jsapi合单支付

* new:合单支付

Co-authored-by: 曾浩 <epdcgsi@dingtalk.com>

weixin-java-pay/src/main/java/com/github/binarywang/wxpay/v3/util/SignUtils.java

@@ -0,0 +1,47 @@
+package com.github.binarywang.wxpay.v3.util;
+
+import java.security.*;
+import java.util.Base64;
+import java.util.Random;
+
+public class SignUtils {
+
+  public static String sign(String string, PrivateKey privateKey){
+    try {
+      Signature sign = Signature.getInstance("SHA256withRSA");
+      sign.initSign(privateKey);
+      sign.update(string.getBytes());
+
+      return Base64.getEncoder().encodeToString(sign.sign());
+    } catch (NoSuchAlgorithmException e) {
+      throw new RuntimeException("当前Java环境不支持SHA256withRSA", e);
+    } catch (SignatureException e) {
+      throw new RuntimeException("签名计算失败", e);
+    } catch (InvalidKeyException e) {
+      throw new RuntimeException("无效的私钥", e);
+    }
+  }
+
+  /**
+   * 随机生成32位字符串.
+   */
+  public static String genRandomStr(){
+    return genRandomStr(32);
+  }
+
+  /**
+   * 生成随机字符串
+   * @param length 字符串长度
+   * @return
+   */
+  public static String genRandomStr(int length) {
+    String base = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+    Random random = new Random();
+    StringBuilder sb = new StringBuilder();
+    for (int i = 0; i < length; i++) {
+      int number = random.nextInt(base.length());
+      sb.append(base.charAt(number));
+    }
+    return sb.toString();
+  }
+}