change auth_filter from string to text

fixes CNVS-21313

test plan
 - db:migrate should pass

Change-Id: I0f61ad9d71a6d3fc4c5d31ecffa685bb7f699000
Reviewed-on: https://gerrit.instructure.com/64008
Tested-by: Jenkins
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>

app/models/account_authorization_config.rb

@@ -21,6 +21,7 @@ require 'net_ldap_extensions'
 
 class AccountAuthorizationConfig < ActiveRecord::Base
   include Workflow
+  validates :auth_filter, length: {maximum: maximum_text_length, allow_nil: true, allow_blank: true}
 
   strong_params
 

db/migrate/20150925063254_change_auth_filter_to_text.rb

@@ -0,0 +1,11 @@
+class ChangeAuthFilterToText < ActiveRecord::Migration
+  tag :postdeploy
+
+  def self.up
+    change_column :account_authorization_configs, :auth_filter, :text
+  end
+
+  def self.down
+    change_column :account_authorization_configs, :auth_filter, :string
+  end
+end