problem: cannot verify signature in browser

solution: support NIST P-256 curve which is supported by browser's webcrypto

testing/simple-upstream/src/main/groovy/testing/CommonHandlers.groovy

@@ -1,13 +1,25 @@
 package testing
 
+import com.fasterxml.jackson.databind.ObjectMapper
+
 class CommonHandlers implements CallHandler {
 
+    ObjectMapper objectMapper
+    ResourceResponse resourceResponse
+
+    CommonHandlers(ObjectMapper objectMapper) {
+        this.objectMapper = objectMapper
+        this.resourceResponse = new ResourceResponse(objectMapper)
+    }
 
     @Override
     Result handle(String method, List<Object> params) {
         if (method == "eth_syncing") {
             return Result.ok(false)
         }
+        if (method == "eth_chainId") {
+            return resourceResponse.respondWith("chain-id.json")
+        }
         return null
     }
 }

testing/simple-upstream/src/main/groovy/testing/SimpleUpstream.groovy

@@ -17,7 +17,7 @@ class SimpleUpstream {
         internalHandler = new InternalHandler()
 
         handlers << new TestcaseHandler(objectMapper)
-        handlers << new CommonHandlers()
+        handlers << new CommonHandlers(objectMapper)
         handlers << new BlocksHandler(objectMapper)
         handlers << new PingPongHandler()
         handlers << internalHandler