Add support for setting forceAuth, comparisonType, bindingUri to the Saml2Client

The Saml2Client assumes default values for forceAuth (false), comparisonType and bindingUri (HTTP-POST). This patch allows the applications to customize these options.
I would do the opposite and use equals instead of equalsIgnoreCase since we want exact configuration: SAMLConstants.SAML2_POST_BINDING_URI.equals(bindingType)