Assert the validness of generate_sp_desciptor_id

In cases where a consumer may override this option we don't assert the
value. This could cause potential issues.

Signed-off-by: Wesley Schwengle <waterkip@cpan.org>

lib/Net/SAML2/SP.pm

@@ -19,6 +19,7 @@ use Net::SAML2::Protocol::LogoutRequest;
 use Net::SAML2::Util ();
 use URN::OASIS::SAML2 qw(:bindings :urn);
 use XML::Generator;
+use Net::SAML2::Types qw(XsdID);
 
 # ABSTRACT: SAML Service Provider object
 
@@ -569,11 +570,14 @@ sub generate_metadata {
         $error_uri = $self->url . $self->error_url;
     }
 
+    my $id = $self->generate_sp_desciptor_id();
+    XsdID->assert_valid($id);
+
     return $x->xml( $x->EntityDescriptor(
         $md,
         {
             entityID => $self->id,
-            ID       => $self->generate_sp_desciptor_id(),
+            ID       => $id,
         },
         $x->SPSSODescriptor(
             $md,