Add admin sign in page

* Next step is to hook up this button to work
* This provides a skeleton page + test

app/controllers/admin/sign_ins_controller.rb

@@ -0,0 +1,3 @@
+class Admin::SignInsController < ApplicationController
+  def show; end
+end

app/controllers/application_controller.rb

@@ -20,7 +20,11 @@ class ApplicationController < ActionController::Base
 
   rescue_from 'UnauthorizedError::RedirectToLogin' do
     store_location
-    redirect_to sign_in_path
+    if store_location == "/admin"
+      redirect_to admin_sign_in_path
+    else
+      redirect_to sign_in_path
+    end
   end
 
   rescue_from 'UnauthorizedError::UserNotFound' do |error|

app/controllers/saml_authentications_controller.rb

@@ -4,11 +4,7 @@ def create
 
     if user
       session[:user_id] = user.id
-
-      redirect_to(
-        admin_path,
-        notice: t('omniauth_callbacks.success')
-      )
+      redirect_to admin_path, notice: t('omniauth_callbacks.success')
     else
       redirect_to(
         root_path,

app/views/admin/sign_ins/show.html.erb

@@ -0,0 +1,17 @@
+<% content_for :title do %>18F Micro-purchase - Admin Login<% end %>
+
+<div class="usa-grid">
+  <div class="usa-width-one-half">
+    <h1>Admin sign in</h1>
+    <p>
+      <%= link_to 'Authorize with GitHub',
+        '/auth/github',
+        class: 'usa-button usa-button usa-button-outline' %>
+    </p>
+    <div class="mb1 right-align login_gov">
+      <button type="submit" class="btn btn-outline bg-white navy">
+        Authorize with Login.gov
+      </button>
+    </div>
+  </div>
+</div>

config/routes.rb

@@ -3,8 +3,6 @@
     mount LetterOpenerWeb::Engine => "letter_opener"
   end
 
-  # Web requests
-
   root 'auctions#index'
 
   get '/auth/github/callback', to: 'authentications#create'
@@ -18,6 +16,7 @@
   get '/auctions/rules/sealed-bid', to: 'auctions#sealed_bid_auction_rules'
   get '/auctions/rules/reverse', to: 'auctions#reverse_auction_rules'
   get '/admin', to: 'admin/auctions/needs_attention#index'
+  get '/admin/sign_in', to: 'admin/sign_ins#show'
   get '/sign_up', to: 'sign_ups#show'
   get '/sign_in', to: 'sign_ins#show'
 

features/admin_signs_in.feature

@@ -6,3 +6,7 @@ Feature: Admin signs in
     Given I am an administrator
     And I sign in
     Then I should be on the admin needs attention auctions page
+
+  Scenario: Logged out admin tries to visit admin path
+    When I visit the admin page
+    Then I should on the admin login page

features/step_definitions/navigation_steps.rb

@@ -153,3 +153,7 @@
 Then(/^I should be on the rules page for sealed-bid auctions$/) do
   expect(page.current_path).to eq('/auctions/rules/sealed-bid')
 end
+
+Then(/^I should on the admin login page$/) do
+  expect(page.current_path).to eq(admin_sign_in_path)
+end