diff --git a/testing/testclient/testclient.go b/testing/testclient/testclient.go
index 54cdafa..199ff8f 100644
--- a/testing/testclient/testclient.go
+++ b/testing/testclient/testclient.go
@@ -5,8 +5,13 @@ package main
 import (
 	"flag"
 	"io/ioutil"
+	"math/big"
 
+	"github.com/celer-network/agent-pay/celersdk"
+	"github.com/celer-network/agent-pay/common"
+	"github.com/celer-network/agent-pay/ctype"
 	"github.com/celer-network/agent-pay/webapi"
+	"github.com/celer-network/goutils/eth"
 	"github.com/celer-network/goutils/log"
 )
 
@@ -29,6 +34,27 @@ func main() {
 		log.Fatal(err)
 	}
 	log.Infoln("start testclient on port", *grpcPort, "using ks", *ksPath)
+	if *extSigner {
+		addr, priv, err := eth.GetAddrPrivKeyFromKeystore(string(ksBytes), "")
+		if err != nil {
+			log.Fatal(err)
+		}
+		p := common.Bytes2Profile(cfg)
+		signer, err := eth.NewSigner(priv, big.NewInt(p.ChainId))
+		if err != nil {
+			log.Fatal(err)
+		}
+		webapi.NewInternalApiServerWithExternalSigner(
+			-1,
+			*grpcPort,
+			"http://localhost:*",
+			ctype.Addr2Hex(addr),
+			*dataPath,
+			string(cfg[:]),
+			&testExternalSigner{Signer: signer},
+			nil).Start()
+		return
+	}
 	webapi.NewInternalApiServer(
 		-1,
 		*grpcPort,
@@ -36,6 +62,19 @@ func main() {
 		string(ksBytes[:]),
 		"",
 		*dataPath,
-		string(cfg[:]),
-		*extSigner).Start()
+		string(cfg[:])).Start()
+}
+
+type testExternalSigner struct {
+	eth.Signer
+}
+
+func (es *testExternalSigner) OnSignMessage(reqid int, msg []byte) {
+	res, _ := es.SignEthMessage(msg)
+	celersdk.PublishSignedResult(reqid, res)
+}
+
+func (es *testExternalSigner) OnSignTransaction(reqid int, rawtx []byte) {
+	res, _ := es.SignEthTransaction(rawtx)
+	celersdk.PublishSignedResult(reqid, res)
 }
diff --git a/webapi/api_server.go b/webapi/api_server.go
index 486fb06..999e3cb 100644
--- a/webapi/api_server.go
+++ b/webapi/api_server.go
@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"math/big"
 	"net"
 	"net/http"
 	"strconv"
@@ -17,12 +16,10 @@ import (
 
 	"github.com/celer-network/agent-pay/celersdk"
 	"github.com/celer-network/agent-pay/celersdkintf"
-	"github.com/celer-network/agent-pay/common"
 	"github.com/celer-network/agent-pay/ctype"
 	"github.com/celer-network/agent-pay/entity"
 	msgrpc "github.com/celer-network/agent-pay/rpc"
 	"github.com/celer-network/agent-pay/webapi/rpc"
-	"github.com/celer-network/goutils/eth"
 	"github.com/celer-network/goutils/log"
 	"github.com/improbable-eng/grpc-web/go/grpcweb"
 	"github.com/rs/cors"
@@ -44,23 +41,6 @@ type ApiServer struct {
 	appSessionMapLock sync.Mutex
 }
 
-// implement celersdk.ExternalSignerCallback interface
-// also embed eth.Signer so celersdk.ExternalSignerManager can tell the difference and
-// avoid double hash
-type extSigner struct {
-	eth.Signer
-}
-
-func (es *extSigner) OnSignMessage(reqid int, msg []byte) {
-	res, _ := es.SignEthMessage(msg)
-	celersdk.PublishSignedResult(reqid, res)
-}
-
-func (es *extSigner) OnSignTransaction(reqid int, rawtx []byte) {
-	res, _ := es.SignEthTransaction(rawtx)
-	celersdk.PublishSignedResult(reqid, res)
-}
-
 func NewApiServer(
 	webPort int,
 	grpcPort int,
@@ -68,8 +48,34 @@ func NewApiServer(
 	keystore string,
 	password string,
 	dataPath string,
+	config string) *ApiServer {
+	return newApiServerWithClientInit(webPort, grpcPort, allowedOrigins, func(callbackImpl *callbackImpl) {
+		go celersdk.InitClient(
+			&celersdk.Account{Keystore: keystore, Password: password},
+			config,
+			dataPath,
+			callbackImpl)
+	})
+}
+
+func NewApiServerWithExternalSigner(
+	webPort int,
+	grpcPort int,
+	allowedOrigins string,
+	addr string,
+	dataPath string,
 	config string,
-	useExtSigner bool) *ApiServer {
+	signcb celersdk.ExternalSignerCallback) *ApiServer {
+	return newApiServerWithClientInit(webPort, grpcPort, allowedOrigins, func(callbackImpl *callbackImpl) {
+		go celersdk.InitClientWithSigner(addr, config, dataPath, callbackImpl, signcb)
+	})
+}
+
+func newApiServerWithClientInit(
+	webPort int,
+	grpcPort int,
+	allowedOrigins string,
+	initClient func(*callbackImpl)) *ApiServer {
 	callbackImpl := NewCallbackImpl()
 	s := &ApiServer{
 		webPort:        webPort,
@@ -78,24 +84,7 @@ func NewApiServer(
 		callbackImpl:   callbackImpl,
 		appSessionMap:  make(map[string]*celersdk.AppSession),
 	}
-	if !useExtSigner {
-		go celersdk.InitClient(
-			&celersdk.Account{Keystore: keystore, Password: password},
-			config,
-			dataPath,
-			callbackImpl)
-	} else { // exercise external signer code path
-		addr, priv, err := eth.GetAddrPrivKeyFromKeystore(keystore, password)
-		if err != nil {
-			log.Fatal(err)
-		}
-		p := common.Bytes2Profile([]byte(config))
-		signer, err := eth.NewSigner(priv, big.NewInt(p.ChainId))
-		if err != nil {
-			log.Fatal(err)
-		}
-		go celersdk.InitClientWithSigner(ctype.Addr2Hex(addr), config, dataPath, callbackImpl, &extSigner{signer})
-	}
+	initClient(callbackImpl)
 
 	select {
 	case client := <-callbackImpl.clientReady:
diff --git a/webapi/cmd/main.go b/webapi/cmd/main.go
index a82d46d..bca7040 100644
--- a/webapi/cmd/main.go
+++ b/webapi/cmd/main.go
@@ -73,5 +73,5 @@ func main() {
 		string(ksBytes[:]),
 		ksPasswordStr,
 		*dataPath,
-		string(cfg[:]), false).Start()
+		string(cfg[:])).Start()
 }
diff --git a/webapi/internal_api_server.go b/webapi/internal_api_server.go
index 0bbabef..d11e4f4 100644
--- a/webapi/internal_api_server.go
+++ b/webapi/internal_api_server.go
@@ -14,6 +14,7 @@ import (
 
 type InternalApiServer struct {
 	*ApiServer
+	register func(*grpc.Server)
 }
 
 func NewInternalApiServer(
@@ -23,14 +24,29 @@ func NewInternalApiServer(
 	keystore string,
 	password string,
 	dataPath string,
+	config string) *InternalApiServer {
+	apiServer := NewApiServer(webPort, grpcPort, allowedOrigins, keystore, password, dataPath, config)
+	return &InternalApiServer{ApiServer: apiServer}
+}
+
+func NewInternalApiServerWithExternalSigner(
+	webPort int,
+	grpcPort int,
+	allowedOrigins string,
+	addr string,
+	dataPath string,
 	config string,
-	extSigner bool) *InternalApiServer {
-	apiServer := NewApiServer(webPort, grpcPort, allowedOrigins, keystore, password, dataPath, config, extSigner)
-	return &InternalApiServer{apiServer}
+	cb celersdk.ExternalSignerCallback,
+	register func(*grpc.Server)) *InternalApiServer {
+	apiServer := NewApiServerWithExternalSigner(webPort, grpcPort, allowedOrigins, addr, dataPath, config, cb)
+	return &InternalApiServer{ApiServer: apiServer, register: register}
 }
 
 func (s *InternalApiServer) Start() {
 	gs := grpc.NewServer()
+	if s.register != nil {
+		s.register(gs)
+	}
 	rpc.RegisterWebApiServer(gs, s.ApiServer)
 	rpc.RegisterInternalWebApiServer(gs, s)
 	s.ApiServer.serve(gs)