FEATURE: Experimental support for group membership via google auth (#14835)

This commit introduces a new site setting "google_oauth2_hd_groups". If enabled, group information will be fetched from Google during authentication, and stored in the Discourse database. These 'associated groups' can be connected to a Discourse group via the "Membership" tab of the group preferences UI. 

The majority of the implementation is generic, so we will be able to add support to more authentication methods in the near future.

https://meta.discourse.org/t/managing-group-membership-via-authentication/175950

spec/models/associated_group_spec.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe AssociatedGroup do
+  let(:user) { Fabricate(:user) }
+  let(:associated_group) { Fabricate(:associated_group) }
+  let(:group) { Fabricate(:group) }
+
+  it "generates a label" do
+    ag = described_class.new(name: "group1", provider_name: "google")
+    expect(ag.label).to eq("google:group1")
+  end
+
+  it "detects whether any auth providers provide associated groups" do
+    SiteSetting.enable_google_oauth2_logins = true
+    SiteSetting.google_oauth2_hd = 'domain.com'
+    SiteSetting.google_oauth2_hd_groups = false
+    expect(described_class.has_provider?).to eq(false)
+
+    SiteSetting.google_oauth2_hd_groups = true
+    expect(described_class.has_provider?).to eq(true)
+  end
+
+  context "cleanup!" do
+    before do
+      associated_group.last_used = 8.days.ago
+      associated_group.save
+    end
+
+    it "deletes associated groups not used in over a week" do
+      described_class.cleanup!
+      expect(described_class.exists?(associated_group.id)).to eq(false)
+    end
+
+    it "doesnt delete associated groups associated with groups" do
+      GroupAssociatedGroup.create(group_id: group.id, associated_group_id: associated_group.id)
+      described_class.cleanup!
+      expect(described_class.exists?(associated_group.id)).to eq(true)
+    end
+
+    it "doesnt delete associated groups associated with users" do
+      UserAssociatedGroup.create(user_id: user.id, associated_group_id: associated_group.id)
+      described_class.cleanup!
+      expect(described_class.exists?(associated_group.id)).to eq(true)
+    end
+  end
+end