🐛 #3916【小程序】修复同城配送接口RSA签名错误的问题

weixin-java-miniapp/src/main/java/cn/binarywang/wx/miniapp/api/impl/BaseWxMaServiceImpl.java

@@ -908,6 +908,23 @@ public abstract class BaseWxMaServiceImpl<H, P> implements WxMaService, RequestH
     return Base64.getEncoder().encodeToString(data);
   }
 
+  /**
+   * 构造 RSA 待签名串。
+   *
+   * <p>根据微信官方 API 签名规范，待签名串格式为：<br>
+   * {@code urlpath\nappid\ntimestamp\npostdata}<br>
+   * 字段之间使用换行符 {@code \n} 分隔，共 4 个字段，末尾无额外回车符。
+   *
+   * @param urlPath     当前请求 API 的 URL，不含 Query 参数
+   * @param appId       小程序 AppId
+   * @param timestamp   签名时的时间戳
+   * @param postData    加密后的请求 POST 数据（JSON 字符串）
+   * @return 拼接好的待签名串
+   */
+  static String buildSignaturePayload(String urlPath, String appId, long timestamp, String postData) {
+    return urlPath + "\n" + appId + "\n" + timestamp + "\n" + postData;
+  }
+
   @Override
   public String postWithSignature(String url, JsonObject jsonObject) throws WxErrorException {
     long timestamp = System.currentTimeMillis() / 1000;
@@ -962,8 +979,8 @@ public abstract class BaseWxMaServiceImpl<H, P> implements WxMaService, RequestH
       reqData.addProperty("authtag", base64Encode(authTag));
       String requestJson = reqData.toString();
 
-      // 计算签名 RSA
+      // 计算签名 RSA，待签名串格式：urlpath\nappid\ntimestamp\npostdata
-      String payload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + rsaKeySn + "\n" + requestJson;
+      String payload = buildSignaturePayload(urlPath, appId, timestamp, requestJson);
       byte[] dataBuffer = payload.getBytes(StandardCharsets.UTF_8);
       RSAPrivateKey priKey;
       try {

weixin-java-miniapp/src/test/java/cn/binarywang/wx/miniapp/api/impl/WxMaSignaturePayloadTest.java

@@ -0,0 +1,71 @@
+package cn.binarywang.wx.miniapp.api.impl;
+
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertFalse;
+
+import org.testng.annotations.Test;
+
+/**
+ * 验证同城配送 API 签名 payload 格式的单元测试。
+ *
+ * <p>直接测试 {@link BaseWxMaServiceImpl#buildSignaturePayload} 生产方法，
+ * 确保待签名串格式符合微信官方规范：<br>
+ * {@code urlpath\nappid\ntimestamp\npostdata}<br>
+ * 共 4 个字段，字段间以换行符 {@code \n} 分隔，末尾无额外回车符。
+ *
+ * @author GitHub Copilot
+ * @see <a
+ *     href="https://developers.weixin.qq.com/miniprogram/dev/OpenApiDoc/getting_started/api_signature.html">
+ *     微信服务端API签名指南</a>
+ */
+public class WxMaSignaturePayloadTest {
+
+  private static final String URL_PATH =
+      "https://api.weixin.qq.com/cgi-bin/express/intracity/createstore";
+  private static final String APP_ID = "wx1234567890abcdef";
+  private static final long TIMESTAMP = 1700000000L;
+  private static final String POST_DATA = "{\"iv\":\"abc\",\"data\":\"xyz\",\"authtag\":\"tag\"}";
+  private static final String RSA_KEY_SN = "some_serial_number";
+
+  /**
+   * 验证 buildSignaturePayload 返回的待签名串恰好包含 4 个字段，
+   * 格式为：urlpath\nappid\ntimestamp\npostdata
+   */
+  @Test
+  public void testPayloadHasExactlyFourFields() {
+    String payload =
+        BaseWxMaServiceImpl.buildSignaturePayload(URL_PATH, APP_ID, TIMESTAMP, POST_DATA);
+
+    String[] parts = payload.split("\n", -1);
+    assertEquals(parts.length, 4, "待签名串应恰好包含 4 个字段（urlpath、appid、timestamp、postdata）");
+    assertEquals(parts[0], URL_PATH, "第 1 段应为 urlpath");
+    assertEquals(parts[1], APP_ID, "第 2 段应为 appid");
+    assertEquals(parts[2], String.valueOf(TIMESTAMP), "第 3 段应为 timestamp");
+    assertEquals(parts[3], POST_DATA, "第 4 段应为 postdata");
+  }
+
+  /**
+   * 验证 buildSignaturePayload 返回的待签名串不包含 rsaKeySn。
+   * rsaKeySn 应通过请求头 Wechatmp-Serial 传递，而不应出现在签名 payload 中。
+   */
+  @Test
+  public void testPayloadDoesNotContainRsaKeySn() {
+    String payload =
+        BaseWxMaServiceImpl.buildSignaturePayload(URL_PATH, APP_ID, TIMESTAMP, POST_DATA);
+
+    assertFalse(payload.contains(RSA_KEY_SN),
+        "待签名串不应包含 rsaKeySn，rsaKeySn 应通过请求头 Wechatmp-Serial 传递");
+  }
+
+  /**
+   * 验证 buildSignaturePayload 返回的待签名串与预期格式完全一致。
+   */
+  @Test
+  public void testPayloadMatchesExpectedFormat() {
+    String expected = URL_PATH + "\n" + APP_ID + "\n" + TIMESTAMP + "\n" + POST_DATA;
+    String actual =
+        BaseWxMaServiceImpl.buildSignaturePayload(URL_PATH, APP_ID, TIMESTAMP, POST_DATA);
+
+    assertEquals(actual, expected, "待签名串格式应为：urlpath\\nappid\\ntimestamp\\npostdata");
+  }
+}