* Improvements to SSO Authorization and logout handling
Changes:
* Adds support for a default access level in the SSO authorization
plugin when group mapping is enabled.
* Restore functionality of the auth_logout_handler configuration option,
allowing the user to be redirected to a configured URL to complete
logout from an external IdP.
* Documentation and test coverage updates
* Set sso.static_level to 0 in AuthSSOTest:testGroupParsing()
* Simplify implementation to use default values in Config::get()