Restrict the dependency proxy auth service

Any objects other than `User` (such as `DeployToken`) are not allowed

Changelog: security

app/services/auth/dependency_proxy_authentication_service.rb

@@ -8,7 +8,10 @@ module Auth
 
     def execute(authentication_abilities:)
       return error('dependency proxy not enabled', 404) unless ::Gitlab.config.dependency_proxy.enabled
-      return error('access forbidden', 403) unless current_user
+
+      # Because app/controllers/concerns/dependency_proxy/auth.rb consumes this
+      # JWT only as `User.find`, we currently only allow User (not DeployToken, etc)
+      return error('access forbidden', 403) unless current_user.is_a?(User)
 
       { token: authorized_token.encoded }
     end

changelogs/unreleased/security-10io-dependency-proxy-and-deploy-tokens.yml

+---
+title: Do not allow deploy tokens in the dependency proxy authentication service
+merge_request:
+author:
+type: security

spec/requests/jwt_controller_spec.rb

@@ -263,25 +263,21 @@ RSpec.describe JwtController do
       let(:credential_user) { group_deploy_token.username }
       let(:credential_password) { group_deploy_token.token }
 
-      it_behaves_like 'with valid credentials'
+      it_behaves_like 'returning response status', :forbidden
     end
 
     context 'with project deploy token' do
       let(:credential_user) { project_deploy_token.username }
       let(:credential_password) { project_deploy_token.token }
 
-      it_behaves_like 'with valid credentials'
+      it_behaves_like 'returning response status', :forbidden
     end
 
     context 'with invalid credentials' do
       let(:credential_user) { 'foo' }
       let(:credential_password) { 'bar' }
 
-      it 'returns unauthorized' do
-        subject
-
-        expect(response).to have_gitlab_http_status(:unauthorized)
-      end
+      it_behaves_like 'returning response status', :unauthorized
     end
   end
 

spec/services/auth/dependency_proxy_authentication_service_spec.rb

@@ -13,28 +13,31 @@ RSpec.describe Auth::DependencyProxyAuthenticationService do
   describe '#execute' do
     subject { service.execute(authentication_abilities: nil) }
 
+    shared_examples 'returning' do |status:, message:|
+      it "returns #{message}", :aggregate_failures do
+        expect(subject[:http_status]).to eq(status)
+        expect(subject[:message]).to eq(message)
+      end
+    end
+
     context 'dependency proxy is not enabled' do
       before do
         stub_config(dependency_proxy: { enabled: false })
       end
 
-      it 'returns not found' do
-        result = subject
-
-        expect(result[:http_status]).to eq(404)
-        expect(result[:message]).to eq('dependency proxy not enabled')
-      end
+      it_behaves_like 'returning', status: 404, message: 'dependency proxy not enabled'
     end
 
     context 'without a user' do
       let(:user) { nil }
 
-      it 'returns forbidden' do
-        result = subject
+      it_behaves_like 'returning', status: 403, message: 'access forbidden'
+    end
+
+    context 'with a deploy token as user' do
+      let_it_be(:user) { create(:deploy_token) }
 
-        expect(result[:http_status]).to eq(403)
-        expect(result[:message]).to eq('access forbidden')
-      end
+      it_behaves_like 'returning', status: 403, message: 'access forbidden'
     end
 
     context 'with a user' do