add route for /saml2 to get metadata

it's a SAML convention that metadata be returned from the URI of
then entity ID. also publicize this URL in authentication settings

Change-Id: If18eca61d2259cdac77c398cc957f7b77f5217d7
Reviewed-on: https://gerrit.instructure.com/76436
Tested-by: Jenkins
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

app/models/account_authorization_config/saml.rb

@@ -55,6 +55,10 @@ class AccountAuthorizationConfig::SAML < AccountAuthorizationConfig::Delegated
     [nil, self]
   end
 
+  def entity_id
+    super || saml_default_entity_id
+  end
+
   def set_saml_defaults
     self.entity_id ||= saml_default_entity_id
     self.requested_authn_context = nil if self.requested_authn_context.blank?

app/views/account_authorization_configs/_saml_fields.html.erb

@@ -1,3 +1,8 @@
+<p><%= mt(<<-TEXT, metadata_url: link_to(aac.entity_id, aac.entity_id))
+The Canvas SAML Entity ID is %{metadata_url}, and the Service Provider metadata
+is available at that URL.
+TEXT
+%></p>
 <% css_bundle :saml_fields %>
 <div class="ic-Form-control">
   <%= f.label :idp_entity_id, t('IdP Entity ID'), class: 'ic-Label' %>

config/routes.rb

@@ -816,6 +816,7 @@ CanvasRails::Application.routes.draw do
   get 'browserconfig.xml', to: 'info#browserconfig', defaults: { format: 'xml' }
 
   post 'object_snippet' => 'context#object_snippet'
+  get 'saml2' => 'accounts#saml_meta_data'
   get 'saml_meta_data' => 'accounts#saml_meta_data'
 
   # Routes for course exports

db/migrate/20120106220543_set_saml_entity_id.rb

@@ -12,7 +12,7 @@ class SetSamlEntityId < ActiveRecord::Migration
     end
     
     AccountAuthorizationConfig.where(auth_type: "saml").each do |aac|
-      if aac.entity_id.blank?
+      if aac['entity_id'].blank?
         aac.entity_id = old_default_domain || aac.saml_default_entity_id
         aac.save!
       end