Add OAuth2 authentication (#147)

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

app/models/o_auth.rb

@@ -0,0 +1,30 @@
+class OAuth < ApplicationRecord
+  include TenantOwnable
+  include ApplicationHelper
+  include Rails.application.routes.url_helpers
+
+  attr_accessor :state
+
+  validates :name, presence: true, uniqueness: { scope: :tenant_id }
+  validates :is_enabled, inclusion: { in: [true, false] }
+  validates :client_id, presence: true
+  validates :client_secret, presence: true
+  validates :authorize_url, presence: true
+  validates :token_url, presence: true
+  validates :profile_url, presence: true
+  validates :scope, presence: true
+  validates :json_user_email_path, presence: true
+
+  def callback_url
+    add_subdomain_to(method(:o_auth_callback_url), id)
+  end
+
+  def authorize_url_with_query_params
+    "#{authorize_url}?"\
+    "response_type=code&"\
+    "client_id=#{client_id}&"\
+    "redirect_uri=#{callback_url()}&"\
+    "scope=#{scope}&"\
+    "state=#{state}"
+  end
+end