Add Azure Active Directory login

![Login page screenshot](https://user-images.githubusercontent.com/1086421/51774269-b17b4900-20bf-11e9-96d1-09625ffd19e4.png)

app/app/settings.py

@@ -92,12 +92,17 @@ WSGI_APPLICATION = 'app.wsgi.application'
 
 AUTHENTICATION_BACKENDS = [
     'social_core.backends.github.GithubOAuth2',
+    'social_core.backends.azuread_tenant.AzureADTenantOAuth2',
     'django.contrib.auth.backends.ModelBackend',
 ]
 
 SOCIAL_AUTH_GITHUB_KEY = os.getenv('OAUTH_GITHUB_KEY')
 SOCIAL_AUTH_GITHUB_SECRET = os.getenv('OAUTH_GITHUB_SECRET')
 
+SOCIAL_AUTH_AZUREAD_TENANT_OAUTH2_KEY = os.getenv('OAUTH_AAD_KEY')
+SOCIAL_AUTH_AZUREAD_TENANT_OAUTH2_SECRET = os.getenv('OAUTH_AAD_SECRET')
+SOCIAL_AUTH_AZUREAD_TENANT_OAUTH2_TENANT_ID = os.getenv('OAUTH_AAD_TENANT')
+
 # Database
 # https://docs.djangoproject.com/en/2.0/ref/settings/#databases
 

app/server/templates/login.html

@@ -53,11 +53,17 @@
         <div class="is-divider" data-content="OR"></div>
         {% endif %}
         {% if github_login %}
-        <a href="{% url 'social:begin' 'github' %}" class="button is-fullwidth is-middle">
+        <a href="{% url 'social:begin' 'github' %}" class="button is-fullwidth mb10">
           <span class="icon"><i class="fab fa-github"></i></span>
           <span>Login with Github</span>
         </a>
         {% endif %}
+        {% if aad_login %}
+        <a href="{% url 'social:begin' 'azuread-tenant-oauth2' %}" class="button is-fullwidth mb10">
+          <span class="icon"><i class="fab fa-microsoft"></i></span>
+          <span>Login with Active Directory</span>
+        </a>
+        {% endif %}
       </div>
     </div>
   </div>

app/server/views.py

@@ -185,6 +185,7 @@ class LoginView(BaseLoginView):
     redirect_authenticated_user = True
     extra_context = {
         'github_login': bool(settings.SOCIAL_AUTH_GITHUB_KEY),
+        'aad_login': bool(settings.SOCIAL_AUTH_AZUREAD_TENANT_OAUTH2_TENANT_ID),
     }
 
     def get_context_data(self, **kwargs):

requirements.txt

@@ -13,7 +13,7 @@ python-dateutil==2.7.3
 pytz==2018.4
 six==1.11.0
 social-auth-app-django==3.1.0
-social-auth-core==3.0.0
+social-auth-core[azuread]==3.0.0
 text-unidecode==1.2
 tornado==5.0.2
 whitenoise==3.3.1