Add OAuth2 authentication (#147)

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

app/workflows/OAuthSignInUser.rb

@@ -0,0 +1,59 @@
+class OAuthSignInUser
+  include OAuthsHelper
+
+  attr_accessor :user_profile, :o_auth
+
+  # Given:
+  #   user_profile: ruby Hash containing information about the user
+  #                 Could've been returned from OAuthExchangeAuthCodeForProfile
+  #   o_auth: ActiveRecord model with information about the OAuth provider
+  #
+  # The workfow creates a new user if it doesn't exist, or select the existing one
+  # NOTE: it does NOT actually sign in the user, but rather returns it to the controller
+  # where it'll be signed in
+  #
+  # Returns:
+  #   the user, if successful
+  #   nil, if unsuccessful
+
+  def initialize(user_profile: "", o_auth: "")
+    @user_profile = user_profile
+    @o_auth = o_auth
+  end
+
+  def run
+    return nil unless @o_auth and @o_auth.class == OAuth and @o_auth.is_enabled?
+    return nil unless @user_profile and @user_profile.class == Hash
+
+    begin
+      # Attempts to get email from user_profile Hash
+      email = query_path_from_hash(@user_profile, @o_auth.json_user_email_path)
+      
+      return nil if email.nil? or not URI::MailTo::EMAIL_REGEXP.match?(email)
+
+      # Select existing / create new user
+      user = User.find_by(email: email)
+      
+      if user.nil?
+        if not @o_auth.json_user_name_path.blank?
+          full_name = query_path_from_hash(@user_profile, @o_auth.json_user_name_path)
+        end
+        full_name ||= I18n.t('defaults.user_full_name')
+
+        user = User.new(
+          email: email,
+          full_name: full_name,
+          password: Devise.friendly_token,
+          status: 'active'
+        )
+        user.skip_confirmation!
+        user.save
+      end
+
+      return user
+    rescue => error
+      print(error)
+      return nil
+    end
+  end
+end