Add OAuth2 authentication (#147)

- Added Site settings > Authentication section
- Create/edit/delete your custom oauth2 configurations
- Login or signup with oauth2

Gemfile.lock

@@ -98,6 +98,9 @@ GEM
     ffi (1.15.5)
     globalid (1.0.0)
       activesupport (>= 5.0)
+    httparty (0.18.0)
+      mime-types (~> 3.0)
+      multi_xml (>= 0.5.2)
     i18n (1.10.0)
       concurrent-ruby (~> 1.0)
     i18n-js (3.9.2)
@@ -129,10 +132,14 @@ GEM
     marcel (1.0.2)
     matrix (0.4.2)
     method_source (1.0.0)
+    mime-types (3.4.1)
+      mime-types-data (~> 3.2015)
+    mime-types-data (3.2022.0105)
     mini_mime (1.1.2)
     mini_portile2 (2.8.0)
     minitest (5.15.0)
     msgpack (1.5.2)
+    multi_xml (0.6.0)
     nio4r (2.5.8)
     nokogiri (1.13.6)
       mini_portile2 (~> 2.8.0)
@@ -275,6 +282,7 @@ DEPENDENCIES
   capybara (>= 2.15)
   devise (= 4.7.3)
   factory_bot_rails (~> 5.0.2)
+  httparty (= 0.18.0)
   i18n-js
   jbuilder (~> 2.7)
   kaminari (~> 1.2.1)