Some of the WIF configuration elements support extensibility. This means that you can attach arbitrary XML child elements to the configuration elements. When this is the case, the WIF configuration system creates the piece of plumbing in question using a special ctor that takes an XmlNodeList representing the custom configuration. You can then parse the XML and configure the class accordingly. Examples are:

IssuerNameRegistry

<issuerNameRegistry type=“ConfigurationBasedIssuerNameRegistry, …“>
  <trustedIssuers>
    <add name=“foo“
         thumbprint=“xxx“ />
  </trustedIssuers>
</issuerNameRegistry>

ClaimsAuthorizationManager
(see here)

<claimsAuthorizationManager type=“PolicyBasedAuthorizationManager“>
  <policy resource=“Directory“
          action=“Browse“>
    <claim claimType=”…”
           claimValue=“Users“ />
  </policy>
</claimsAuthorizationManager>

SecurityTokenHandler
(see here)

<add type=“Saml11SecurityTokenHandler, …“>
  <samlSecurityTokenRequirement issuerCertificateRevocationMode=“Online“
                                issuerCertificateValidationMode=“ChainTrust“ />
</add>