Represents a SAML AuthnRequest message.
Ported from the Erlang esaml_authnreq record.
esaml_authnreq
@type t() :: %ExSaml.Core.AuthnRequest{ consumer_location: String.t(), destination: String.t(), issue_instant: String.t(), issuer: String.t(), name_format: String.t() | nil, version: String.t() }