save avatar works.

apiV1Avatar.go

 	"encoding/base64"
 	"fmt"
 	"github.com/brianvoe/gofakeit/v6"
+	log "github.com/sirupsen/logrus"
 	"io"
+	"io/ioutil"
 	"net/http"
 	"os"
 	"strings"
 	idx := fmt.Sprintf("%d%s", number, gender)
 	return dummyAvatar[idx]
 }
+
+func apiV1AvatarPost(w http.ResponseWriter, r *http.Request, ss *loan.Session) {
+	prefix := apiV1Prefix + "avatar/"
+	id := r.URL.Path[len(prefix):]
+
+	body, e := ioutil.ReadAll(r.Body)
+	if e != nil {
+		log.Error("invalid request body for updating avatar ", id, " err= ", e.Error())
+		apiV1Client403Error(w, r, ss)
+		return
+	}
+	p := loan.People{}
+	p.Read(id)
+	p.Avatar = string(body)
+	e = p.Write()
+	if e != nil {
+		log.Error("cannot write avatar ", id, " err ", e.Error())
+		apiV1Server500Error(w, r)
+		return
+	}
+
+	apiV1SendJson(true, w, r, ss)
+}

apiv1.go

 			{"GET", "broker/", apiV1BrokerGet},
 			{"POST", "loan/basic/", apiV1LoanSinglePostBasic},
 			{"GET", "avatar/", apiV1Avatar},
+			{"POST", "avatar/", apiV1AvatarPost},
 			{"POST", "reward/", apiV1RewardPost},
 			{"DELETE", "reward/", apiV1RewardDelete},
 			{"GET", "people-list/", apiV1PeopleList},
 			{"GET", "broker/", apiV1BrokerGet},
 			{"POST", "loan/basic/", apiV1LoanSinglePostBasic},
 			{"GET", "avatar/", apiV1Avatar},
+			{"POST", "avatar/", apiV1AvatarPost},
 			{"POST", "reward/", apiV1RewardPost},
 			{"DELETE", "reward/", apiV1RewardDelete},
 			{"GET", "people-list", apiV1PeopleList},