Send rate-limit bypass key to courses.mooc.fi (#599)

Author: nygrenh

app/models/user.rb

@@ -601,7 +601,7 @@ def processing_submissions_count_for_exercise(exercise_name, course_id)
 
   private
     def courses_mooc_fi_connection
-      Faraday.new(request: { open_timeout: 2, timeout: 10 }) do |f|
+      Faraday.new(headers: CoursesMoocFiRateLimitBypass.headers, request: { open_timeout: 2, timeout: 10 }) do |f|
         f.request :json
         f.response :json
       end

app/services/courses_mooc_fi_rate_limit_bypass.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+# Headers for tmc-server's requests to courses.mooc.fi: sp331 skips its per-IP rate limits when this
+# header matches its RATELIMIT_PROTECTION_SAFE_API_KEY, the same shared value as RACK_ATTACK_SAFE_API_KEY.
+module CoursesMoocFiRateLimitBypass
+  HEADER = 'RATELIMIT-PROTECTION-SAFE-API-KEY'
+
+  def self.headers
+    key = ENV['RACK_ATTACK_SAFE_API_KEY']
+    key.present? ? { HEADER => key } : {}
+  end
+end

app/services/courses_mooc_fi_token_introspector.rb

@@ -64,7 +64,7 @@ def request_introspection(token)
         raise Unavailable, 'courses_mooc_fi_base_url, COURSES_MOOC_FI_INTROSPECTION_CLIENT_ID or COURSES_MOOC_FI_INTROSPECTION_SECRET is not set'
       end
 
-      connection = Faraday.new(request: { open_timeout: 2, timeout: 5 }) do |f|
+      connection = Faraday.new(headers: CoursesMoocFiRateLimitBypass.headers, request: { open_timeout: 2, timeout: 5 }) do |f|
         f.request :url_encoded
         f.response :json
       end

spec/models/user_spec.rb

@@ -342,6 +342,18 @@ def stub_courses_mooc_fi_authentication(status:, body:)
       allow(Faraday).to receive(:new).and_return(connection)
     end
 
+    { 'bypass-key' => { 'RATELIMIT-PROTECTION-SAFE-API-KEY' => 'bypass-key' }, '' => {}, nil => {} }.each do |configured, headers|
+      it "sends rate-limit bypass headers #{headers} when RACK_ATTACK_SAFE_API_KEY is #{configured.inspect}" do
+        allow(ENV).to receive(:[]).and_call_original
+        allow(ENV).to receive(:[]).with('RACK_ATTACK_SAFE_API_KEY').and_return(configured)
+        stub_courses_mooc_fi_authentication(status: 200, body: true)
+
+        User.authenticate_with_status('manageduser', 'secret123')
+
+        expect(Faraday).to have_received(:new).with(hash_including(headers: headers))
+      end
+    end
+
     it 'rejects a wrong local password' do
       User.create!(login: 'localuser', password: 'secret123', email: 'localuser@example.com')
       expect(User.authenticate_with_status('localuser', 'wrongpassword').last).to eq(:rejected)

spec/services/courses_mooc_fi_token_introspector_spec.rb

@@ -44,6 +44,18 @@ def introspect
       expect(sent.request_headers['Accept']).to eq('application/json')
     end
 
+    { 'bypass-key' => 'bypass-key', '' => nil, nil => nil }.each do |configured, sent|
+      it "sends rate-limit bypass key #{sent.inspect} when RACK_ATTACK_SAFE_API_KEY is #{configured.inspect}" do
+        allow(ENV).to receive(:[]).and_call_original
+        allow(ENV).to receive(:[]).with('RACK_ATTACK_SAFE_API_KEY').and_return(configured)
+        stub_provider(status: 200, body: active_body)
+
+        introspect
+
+        expect(provider_requests.last.request_headers['RATELIMIT-PROTECTION-SAFE-API-KEY']).to eq(sent)
+      end
+    end
+
     it 'derives the endpoint and issuer from courses_mooc_fi_base_url' do
       allow(SiteSetting).to receive(:value).with('courses_mooc_fi_base_url').and_return('http://project-331.local/')
       provider.post('http://project-331.local/api/v0/main-frontend/oauth/introspect') do