Add validation for SAML request signing certificate

Add support for ForceAuthn in AuthnRequests

Always set @matching_cert, not just when signature is required (18F#46)

Add RequestAuthnContext Comparison attribute getter

Remove HTTParty in favor of Faraday (LG-3524) (18F#41)

**Why**: Consistency across login.gov projects

v0.14.0-18f release

Support Multiple Certs (18F#39)

* Support multiple certs per SP
* Pass around x509s
* Drop fingerprint, it can be derived from the certs
* Set saml_request.service_provider.matching_cert so we can use it later
* Update version

Merge pull request 18F#38 from 18F/add-default-aal-authn-context

add default aal authn context

0.12.1.18f release

Fix NameID formats