Auth method should an explicit option

Currently the auth method used is determined by which of the first in an array of methods happens to be enabled. This is not very intuitive to configure for users and will only get worse as more auth methods are added. This should be an explicit option, for example:

	//
	// Set the authentication.
	// Options include "local" and "ldap"
	//
	// @type     string
	// @default  "local"
	//
	auth: "local",

If the chosen auth method is disabled internally because of incomplete configuration then throw and error at startup.

I ran into this when I was working on creating my own auth method. Making it work to begin with was confusing. I’m willing to make the changes, I just want to see if I should take the effort.

[merlinthp]

I’d like to add SAML2 authentication support to The Lounge. It sounds like this is a good opportunity to make auth methods more properly pluggable. I’m willing to take a look at this.

[xPaw]

@YaManicKill I think it’s easier to just remove private/public definition in favor of auth, so you’d set auth: public (or none) to disable auth.