FEATURE: Retrieve an existing link only invite (#12575)

In Improve invite system, a newly created link only invite cannot
be retrieved via API with the invitee's email once created. A new
route, /invites/retrieve, is introduced to fetch an already
created invite by email address.

app/controllers/invites_controller.rb

@@ -4,7 +4,7 @@ require 'csv'
 
 class InvitesController < ApplicationController
 
-  requires_login only: [:create, :destroy, :destroy_all_expired, :resend_invite, :resend_all_invites, :upload_csv]
+  requires_login only: [:create, :retrieve, :destroy, :destroy_all_expired, :resend_invite, :resend_all_invites, :upload_csv]
 
   skip_before_action :check_xhr, except: [:perform_accept_invitation]
   skip_before_action :preload_json, except: [:show]
@@ -104,6 +104,17 @@ class InvitesController < ApplicationController
     end
   end
 
+  def retrieve
+    params.require(:email)
+
+    invite = Invite.find_by(invited_by: current_user, email: params[:email])
+    raise Discourse::InvalidParameters.new(:email) if invite.blank?
+
+    guardian.ensure_can_invite_to_forum!(nil)
+
+    render_serialized(invite, InviteSerializer, scope: guardian, root: nil, show_emails: params.has_key?(:email))
+  end
+
   def update
     invite = Invite.find_by(invited_by: current_user, id: params[:id])
     raise Discourse::InvalidParameters.new(:id) if invite.blank?

config/routes.rb

@@ -835,6 +835,7 @@ Discourse::Application.routes.draw do
     post "invites/reinvite-all" => "invites#resend_all_invites"
     delete "invites" => "invites#destroy"
     put "invites/show/:id" => "invites#perform_accept_invitation", as: 'perform_accept_invite'
+    get "invites/retrieve" => "invites#retrieve"
 
     resources :export_csv do
       collection do

spec/requests/invites_controller_spec.rb

@@ -252,6 +252,36 @@ describe InvitesController do
     end
   end
 
+  context '#retrieve' do
+    it 'requires to be logged in' do
+      get '/invites/retrieve.json', params: { email: 'test@example.com' }
+      expect(response.status).to eq(403)
+    end
+
+    context 'while logged in' do
+      before do
+        sign_in(user)
+      end
+
+      fab!(:invite) { Fabricate(:invite, invited_by: user, email: 'test@example.com') }
+
+      it 'raises an error when the email is missing' do
+        get '/invites/retrieve.json'
+        expect(response.status).to eq(400)
+      end
+
+      it 'raises an error when the email cannot be found' do
+        get '/invites/retrieve.json', params: { email: 'test2@example.com' }
+        expect(response.status).to eq(400)
+      end
+
+      it 'can retrieve the invite' do
+        get '/invites/retrieve.json', params: { email: 'test@example.com' }
+        expect(response.status).to eq(200)
+      end
+    end
+  end
+
   context '#update' do
     fab!(:invite) { Fabricate(:invite, invited_by: admin, email: 'test@example.com') }