Add /api/v1/admin/domain_allows (#18668)

- `GET /api/v1/admin/domain_allows` lists allowed domains
- `GET /api/v1/admin/domain_allows/:id` shows one by ID
- `DELETE /api/v1/admin/domain_allows/:id` deletes a given domain from the list
  of allowed domains
- `POST /api/v1/admin/domain_allows` to allow a new domain:
  if that domain is already allowed, the existing DomainAllow will be returned

spec/controllers/api/v1/admin/domain_allows_controller_spec.rb

@@ -0,0 +1,118 @@
+require 'rails_helper'
+
+RSpec.describe Api::V1::Admin::DomainAllowsController, type: :controller do
+  render_views
+
+  let(:role)   { 'admin' }
+  let(:user)   { Fabricate(:user, role: role) }
+  let(:scopes) { 'admin:read admin:write' }
+  let(:token)  { Fabricate(:accessible_access_token, resource_owner_id: user.id, scopes: scopes) }
+
+  before do
+    allow(controller).to receive(:doorkeeper_token) { token }
+  end
+
+  shared_examples 'forbidden for wrong scope' do |wrong_scope|
+    let(:scopes) { wrong_scope }
+
+    it 'returns http forbidden' do
+      expect(response).to have_http_status(403)
+    end
+  end
+
+  shared_examples 'forbidden for wrong role' do |wrong_role|
+    let(:role) { wrong_role }
+
+    it 'returns http forbidden' do
+      expect(response).to have_http_status(403)
+    end
+  end
+
+  describe 'GET #index' do
+    let!(:domain_allow) { Fabricate(:domain_allow) }
+
+    before do
+      get :index
+    end
+
+    it_behaves_like 'forbidden for wrong scope', 'write:statuses'
+    it_behaves_like 'forbidden for wrong role', 'user'
+    it_behaves_like 'forbidden for wrong role', 'moderator'
+
+    it 'returns http success' do
+      expect(response).to have_http_status(200)
+    end
+
+    it 'returns the expected domain allows' do
+      json = body_as_json
+      expect(json.length).to eq 1
+      expect(json[0][:id].to_i).to eq domain_allow.id
+    end
+  end
+
+  describe 'GET #show' do
+    let!(:domain_allow) { Fabricate(:domain_allow) }
+
+    before do
+      get :show, params: { id: domain_allow.id }
+    end
+
+    it_behaves_like 'forbidden for wrong scope', 'write:statuses'
+    it_behaves_like 'forbidden for wrong role', 'user'
+    it_behaves_like 'forbidden for wrong role', 'moderator'
+
+    it 'returns http success' do
+      expect(response).to have_http_status(200)
+    end
+
+    it 'returns expected domain name' do
+      json = body_as_json
+      expect(json[:domain]).to eq domain_allow.domain
+    end
+  end
+
+  describe 'DELETE #destroy' do
+    let!(:domain_allow) { Fabricate(:domain_allow) }
+
+    before do
+      delete :destroy, params: { id: domain_allow.id }
+    end
+
+    it_behaves_like 'forbidden for wrong scope', 'write:statuses'
+    it_behaves_like 'forbidden for wrong role', 'user'
+    it_behaves_like 'forbidden for wrong role', 'moderator'
+
+    it 'returns http success' do
+      expect(response).to have_http_status(200)
+    end
+
+    it 'deletes the block' do
+      expect(DomainAllow.find_by(id: domain_allow.id)).to be_nil
+    end
+  end
+
+  describe 'POST #create' do
+    let!(:domain_allow) { Fabricate(:domain_allow, domain: 'example.com') }
+
+    before do
+      post :create, params: { domain: 'foo.bar.com' }
+    end
+
+    it_behaves_like 'forbidden for wrong scope', 'write:statuses'
+    it_behaves_like 'forbidden for wrong role', 'user'
+    it_behaves_like 'forbidden for wrong role', 'moderator'
+
+    it 'returns http success' do
+      expect(response).to have_http_status(200)
+    end
+
+    it 'returns expected domain name' do
+      json = body_as_json
+      expect(json[:domain]).to eq 'foo.bar.com'
+    end
+
+    it 'creates a domain block' do
+      expect(DomainAllow.find_by(domain: 'foo.bar.com')).to_not be_nil
+    end
+  end
+end