diff --git a/README.md b/README.md
index 8c192a7..b2b8b3b 100644
--- a/README.md
+++ b/README.md
@@ -50,7 +50,8 @@ wget https://raw.githubusercontent.com/b4tman/sync_ics2gcal/develop/sample-confi
 * `start_from` - start date:
   * full format datetime, `2018-04-03T13:23:25.000001Z` for example
   * or just `now`
-* `service_account` - service account filename
+* *(Optional)* `service_account` - service account filename, remove it from config to use [default credentials](https://developers.google.com/identity/protocols/application-default-credentials)
+* *(Optional)* `logging` - [config](https://docs.python.org/3.8/library/logging.config.html#dictionary-schema-details) to setup logging
 * `google_id` - target google calendar id, `my-calendar@group.calendar.google.com` for example
 * `source` - source `.ics` filename, `my-calendar.ics` for example
 
diff --git a/sync_ics2gcal/gcal.py b/sync_ics2gcal/gcal.py
index 8481a08..6bc9ed9 100644
--- a/sync_ics2gcal/gcal.py
+++ b/sync_ics2gcal/gcal.py
@@ -14,6 +14,21 @@ class GoogleCalendarService():
         service Resource
     """
 
+    @staticmethod
+    def default():
+        """make service Resource from default credentials (authorize)
+        ( https://developers.google.com/identity/protocols/application-default-credentials )
+        ( https://googleapis.dev/python/google-auth/latest/reference/google.auth.html#google.auth.default )
+
+        Returns:
+            service Resource
+        """
+
+        scopes = ['https://www.googleapis.com/auth/calendar']
+        credentials, _ = google.auth.default(scopes=scopes)
+        service = discovery.build('calendar', 'v3', credentials=credentials)
+        return service
+    
     @staticmethod
     def from_srv_acc_file(service_account_file):
         """make service Resource from service account filename (authorize)
@@ -27,6 +42,26 @@ class GoogleCalendarService():
         scoped_credentials = credentials.with_scopes(scopes)
         service = discovery.build('calendar', 'v3', credentials=scoped_credentials)
         return service
+    
+    @staticmethod
+    def from_config(config):
+        """make service Resource from config dict
+
+        Arguments:
+        config -- dict() config with keys:
+                    (optional) service_account: - service account filename
+                    if key not in dict then default credentials will be used
+                    ( https://developers.google.com/identity/protocols/application-default-credentials )
+
+        Returns:
+            service Resource
+        """
+
+        if 'service_account' in config:
+            service = GoogleCalendarService.from_srv_acc_file(config['service_account'])
+        else:
+            service = GoogleCalendarService.default()
+        return service
 
 def select_event_key(event):
     """select event key for logging
diff --git a/sync_ics2gcal/manage_calendars.py b/sync_ics2gcal/manage_calendars.py
index b1236a2..f457294 100644
--- a/sync_ics2gcal/manage_calendars.py
+++ b/sync_ics2gcal/manage_calendars.py
@@ -86,8 +86,7 @@ def main():
     if 'logging' in config:
         logging.config.dictConfig(config['logging'])
 
-    srv_acc_file = config['service_account']
-    service = GoogleCalendarService.from_srv_acc_file(srv_acc_file)
+    service = GoogleCalendarService.from_config(config)
 
     if 'list' == args.command:
         list_calendars(service)
diff --git a/sync_ics2gcal/sync_calendar.py b/sync_ics2gcal/sync_calendar.py
index 37f5805..814d9d5 100644
--- a/sync_ics2gcal/sync_calendar.py
+++ b/sync_ics2gcal/sync_calendar.py
@@ -34,14 +34,13 @@ def main():
 
     calendarId = config['calendar']['google_id']
     ics_filepath = config['calendar']['source']
-    srv_acc_file = config['service_account']
 
     start = get_start_date(config['start_from'])
 
     converter = CalendarConverter()
     converter.load(ics_filepath)
 
-    service = GoogleCalendarService.from_srv_acc_file(srv_acc_file)
+    service = GoogleCalendarService.from_config(config)
     gcalendar = GoogleCalendar(service, calendarId)
 
     sync = CalendarSync(gcalendar, converter)