feat(example): Allow configuring some parameters with env variables (#663)

Co-authored-by: Andrey Rusakov <andrey.rusakov@camptocamp.com>

example/server/storage/user.go

@@ -2,6 +2,8 @@ package storage
 
 import (
 	"crypto/rsa"
+	"encoding/json"
+	"os"
 	"strings"
 
 	"golang.org/x/text/language"
@@ -35,6 +37,18 @@ type userStore struct {
 	users map[string]*User
 }
 
+func StoreFromFile(path string) (UserStore, error) {
+	users := map[string]*User{}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	if err := json.Unmarshal(data, &users); err != nil {
+		return nil, err
+	}
+	return userStore{users}, nil
+}
+
 func NewUserStore(issuer string) UserStore {
 	hostname := strings.Split(strings.Split(issuer, "://")[1], ":")[0]
 	return userStore{