[authsaml2] set session expiry time in sso_after_response if assertion has a SessionNotOnOrAfter attribute (fixes #737)
[authsaml2] set session expiry time in sso_after_response if assertion has a SessionNotOnOrAfter attribute (fixes #737)

 * Just after the call to django.contrib.auth.login(),
   get_session_not_on_or_after() is called to find some
   SessionNotOnOrAfter attributes and returning their minimum value.

BryceLohr/authentic,pu239ppy/authentic2,BryceLohr/authentic,adieu/authentic2,pu239ppy/authentic2,BryceLohr/authentic,incuna/authentic,adieu/authentic2,BryceLohr/authentic,incuna/authentic,incuna/authentic,incuna/authentic,incuna/authentic,adieu/authentic2,pu239ppy/authentic2,pu239ppy/authentic2,adieu/authentic2