[FR] support multiple IDPs

[FossPrime]

Currently everything is hard wired to read authentication config from authentication.saml which limits IDP servers to one.

In my fork I used `authentication.strateges.filter(s => s instanceOf SamlStrategy) to get a list of all strategies based on SamlStrategy. And then mitigated the global collision, which would ideally be removed by overloading the strategy constructor to accept configuration, and then reading that in the express middleware.