fix(http): handle axios error code UNABLE_TO_VERIFY_LEAF_SIGNATURE (#…

…1267)

- Map error code `UNABLE_TO_VERIFY_LEAF_SIGNATURE` to error code 27
- Map error code `UNABLE_TO_VERIFY_LEAF_SIGNATURE` to error codename `ELEAFSIGNATURE`
- Add documentation for error code 27

docs/src/pages/guides/probes.md

@@ -332,6 +332,7 @@ To make it easier to troubleshoot HTTP requests, we have mapped low-level errors
 | 24   | Request / response size mismatch with Content-Length header value |
 | 25   | Missing HTTP client pool                                          |
 | 26   | Expected error, exact reason is shown on runtime                  |
+| 27   | Unable to verify the first / leaf certificate                     |
 | 99   | Others                                                            |
 | 599  | Connection aborted                                                |
 

src/components/probe/prober/http/request.ts

@@ -423,6 +423,8 @@ function handleAxiosError(
   }
 }
 
+// suppress switch-case complexity since this is dead-simple mapping to error code
+// eslint-disable-next-line complexity
 function getErrorStatusWithExplanation(error: unknown): {
   status: number
   description: string
@@ -573,6 +575,14 @@ function getErrorStatusWithExplanation(error: unknown): {
       }
     }
 
+    case 'UNABLE_TO_VERIFY_LEAF_SIGNATURE': {
+      return {
+        status: 27,
+        description:
+          'ELEAFSIGNATURE: Unable to verify the first / leaf certificate.',
+      }
+    }
+
     default: {
       if (error instanceof AxiosError) {
         log.error(