修复同城配送接口RSA签名payload格式错误（错误码40234）

根据微信官方API签名文档，待签名串格式应为：
urlpath\nappid\ntimestamp\npostdata

原代码错误地在payload中包含了rsaKeySn，导致签名验证失败（40234错误）。
修复：从postWithSignature方法的签名payload中移除rsaKeySn字段。
新增：WxMaSignaturePayloadTest单元测试验证签名格式正确性。

Co-authored-by: binarywang <1343140+binarywang@users.noreply.github.com>

Author: Copilot

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

@@ -962,8 +962,8 @@ public String postWithSignature(String url, JsonObject jsonObject) throws WxErro
       reqData.addProperty("authtag", base64Encode(authTag));
       String requestJson = reqData.toString();
 
-      // 计算签名 RSA
-      String payload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + rsaKeySn + "\n" + requestJson;
+      // 计算签名 RSA，待签名串格式：urlpath\nappid\ntimestamp\npostdata
+      String payload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + 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 +1,112 @@
+package cn.binarywang.wx.miniapp.api.impl;
+
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertTrue;
+
+import java.nio.charset.StandardCharsets;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.Signature;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.MGF1ParameterSpec;
+import java.security.spec.PSSParameterSpec;
+import java.util.Base64;
+import org.testng.annotations.Test;
+
+/**
+ * 验证同城配送 API 签名 payload 格式的单元测试。
+ *
+ * <p>根据微信官方文档，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，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 {
+
+  /**
+   * 验证正确的签名 payload 格式（不含 rsaKeySn）可以通过签名验证，
+   * 即格式为：urlpath\nappid\ntimestamp\npostdata
+   */
+  @Test
+  public void testCorrectSignaturePayloadFormat() throws Exception {
+    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
+    keyGen.initialize(2048);
+    KeyPair keyPair = keyGen.generateKeyPair();
+    RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
+    RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
+
+    String urlPath = "https://api.weixin.qq.com/cgi-bin/express/intracity/createstore";
+    String appId = "wx1234567890abcdef";
+    long timestamp = 1700000000L;
+    String requestJson = "{\"iv\":\"abc\",\"data\":\"xyz\",\"authtag\":\"tag\"}";
+
+    // 正确格式：urlpath\nappid\ntimestamp\npostdata（不含 rsaKeySn）
+    String correctPayload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + requestJson;
+    byte[] dataBuffer = correctPayload.getBytes(StandardCharsets.UTF_8);
+
+    Signature signer = Signature.getInstance("RSASSA-PSS");
+    PSSParameterSpec pssSpec = new PSSParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA256, 32, 1);
+    signer.setParameter(pssSpec);
+    signer.initSign(privateKey);
+    signer.update(dataBuffer);
+    byte[] sigBytes = signer.sign();
+    String signatureStr = Base64.getEncoder().encodeToString(sigBytes);
+
+    // 使用公钥验证签名
+    Signature verifier = Signature.getInstance("RSASSA-PSS");
+    verifier.setParameter(pssSpec);
+    verifier.initVerify(publicKey);
+    verifier.update(dataBuffer);
+    assertTrue(verifier.verify(Base64.getDecoder().decode(signatureStr)),
+        "正确格式的签名应该能通过验证");
+  }
+
+  /**
+   * 验证错误的签名 payload（含 rsaKeySn）签名后，用正确 payload 验证会失败。
+   * 这证明了原来代码中将 rsaKeySn 加入 payload 是错误的。
+   */
+  @Test
+  public void testIncorrectPayloadWithRsaKeySnFails() throws Exception {
+    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
+    keyGen.initialize(2048);
+    KeyPair keyPair = keyGen.generateKeyPair();
+    RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
+    RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
+
+    String urlPath = "https://api.weixin.qq.com/cgi-bin/express/intracity/createstore";
+    String appId = "wx1234567890abcdef";
+    long timestamp = 1700000000L;
+    String rsaKeySn = "some_serial_number";
+    String requestJson = "{\"iv\":\"abc\",\"data\":\"xyz\",\"authtag\":\"tag\"}";
+
+    // 错误格式：payload 中包含了 rsaKeySn（修复前的代码逻辑）
+    String incorrectPayload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + rsaKeySn + "\n" + requestJson;
+    byte[] incorrectData = incorrectPayload.getBytes(StandardCharsets.UTF_8);
+
+    Signature signer = Signature.getInstance("RSASSA-PSS");
+    PSSParameterSpec pssSpec = new PSSParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA256, 32, 1);
+    signer.setParameter(pssSpec);
+    signer.initSign(privateKey);
+    signer.update(incorrectData);
+    byte[] sigBytes = signer.sign();
+    String signatureStr = Base64.getEncoder().encodeToString(sigBytes);
+
+    // 用正确格式的 payload 去验证签名，应该失败
+    String correctPayload = urlPath + "\n" + appId + "\n" + timestamp + "\n" + requestJson;
+    byte[] correctData = correctPayload.getBytes(StandardCharsets.UTF_8);
+
+    Signature verifier = Signature.getInstance("RSASSA-PSS");
+    verifier.setParameter(pssSpec);
+    verifier.initVerify(publicKey);
+    verifier.update(correctData);
+
+    boolean verified = verifier.verify(Base64.getDecoder().decode(signatureStr));
+    assertFalse(verified, "用错误 payload 生成的签名不应该通过正确 payload 的验证，"
+        + "说明 rsaKeySn 不应该包含在签名 payload 中");
+  }
+}