Merge branches 'speedup-auth-fix' and 'require-user-and-pass' into mine

* speedup-auth-fix:
  rubocop
  Squelch rubocop complaints
  Reuse server nonces and account for drbrain/net-http-digest_auth#17

* require-user-and-pass:
  Require username and password to be not nil

lib/faraday/request/digestauth.rb

@@ -31,6 +31,13 @@ class DigestAuth < Faraday::Middleware
       #            - keep_body_on_handshake: if set to truthy, will also send
       #              the original request body
       def initialize(app, user, password, opts = {})
+        if user.nil?
+          raise ArgumentError, 'Username cannot be nil'
+        end
+        if password.nil?
+          raise ArgumentError, 'Password cannot be nil'
+        end
+
         super(app)
         @user = user
         @password = password

spec/faraday/request/digest_auth_spec.rb

@@ -56,4 +56,34 @@
       expect(response.body).to be_empty
     end
   end
+
+  context 'when the username is nil' do
+    let(:connection) do
+      Faraday.new('http://api.example.org/') do |builder|
+        builder.request :digest, nil, 'PASS'
+        builder.adapter :net_http
+      end
+    end
+
+    it 'raises ArgumentError during construction' do
+      expect do
+        connection.get('http://api.example.com')
+      end.to raise_error(ArgumentError, /Username cannot be nil/)
+    end
+  end
+
+  context 'when the password is nil' do
+    let(:connection) do
+      Faraday.new('http://api.example.org/') do |builder|
+        builder.request :digest, 'USER', nil
+        builder.adapter :net_http
+      end
+    end
+
+    it 'raises ArgumentError during construction' do
+      expect do
+        connection.get('http://api.example.com')
+      end.to raise_error(ArgumentError, /Password cannot be nil/)
+    end
+  end
 end