title: When using Shibboleth (v3) as SP , can I map the attribute value in attribute-map.xml?
body: <p>OKTA is IdP and Shibboleth is SP in this setting. 
  OKTA is passing attribute 'roles' something like idp_dev_SLAN_Power, idp_dev_SLAN_Admin, idp_dev_SLAN_account, etc</p>
  
  <p>I am wondering if I can strip 'idp_dev_SLAN_' out when it takes this attribute. </p>
  
  <p>Here is what I see in the current attribute-map.xml. </p>
  
  <pre><code>&lt;Attribute id="roles" name="roles" nameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:unspecified" /&gt;
  </code></pre>
  
  <p>I feel like I can possibly do something with AttributeDecoder. any idea??</p>