FEATURE: Login with Discord (#8053)

This migrates the functionality of discourse-plugin-discord-auth into core. 

The plugin will automatically disable itself when core is updated: fd0867844d

For setup instructions, visit https://meta.discourse.org/t/configuring-discord-login-for-discourse/127129

spec/components/auth/discord_authenticator_spec.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Auth::DiscordAuthenticator do
+  let(:hash) {
+    OmniAuth::AuthHash.new(
+      provider: "facebook",
+      extra: {
+        raw_info: {
+          id: "100",
+          username: "bobbob",
+          guilds: [
+            {
+              "id": "80351110224678912",
+              "name": "1337 Krew",
+              "icon": "8342729096ea3675442027381ff50dfe",
+              "owner": true,
+              "permissions": 36953089
+            }
+          ]
+        }
+      },
+      info: {
+        email: "bob@bob.com",
+        name: "bobbob"
+      },
+      uid: "100"
+    )
+  }
+
+  let(:authenticator) { described_class.new }
+
+  context 'after_authenticate' do
+    it 'works normally' do
+      result = authenticator.after_authenticate(hash)
+      expect(result.user).to eq(nil)
+      expect(result.failed).to eq(false)
+      expect(result.name).to eq("bobbob")
+      expect(result.email).to eq("bob@bob.com")
+    end
+
+    it 'denies access when guilds are restricted' do
+      SiteSetting.discord_trusted_guilds = ["someguildid", "someotherguildid"].join("|")
+      result = authenticator.after_authenticate(hash)
+      expect(result.user).to eq(nil)
+      expect(result.failed).to eq(true)
+      expect(result.failed_reason).to eq(I18n.t("discord.not_in_allowed_guild"))
+    end
+
+    it 'allows access when in an allowed guild' do
+      SiteSetting.discord_trusted_guilds = ["80351110224678912", "anothertrustedguild"].join("|")
+      result = authenticator.after_authenticate(hash)
+      expect(result.user).to eq(nil)
+      expect(result.failed).to eq(false)
+      expect(result.name).to eq("bobbob")
+      expect(result.email).to eq("bob@bob.com")
+    end
+  end
+end