[authsaml2] use load_provider in sso
[authsaml2] use load_provider in sso

It makes autoloading of identity providers metadatass possible.

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