Add stub for irma_configuration downloading

configstore.go

@@ -266,3 +266,7 @@ func (store *ConfigurationStore) Copy(source string, parse bool) error {
 	}
 	return nil
 }
+
+func (store *ConfigurationStore) Download(set *IrmaIdentifierSet) error {
+	return nil
+}

messages.go

@@ -98,6 +98,8 @@ const (
 	ErrorApi = ErrorType("api")
 	// Server returned unexpected or malformed response
 	ErrorServerResponse = ErrorType("serverResponse")
+	// Error during downloading of credential type, issuer, or public keys
+	ErrorConfigurationStoreDownload = ErrorType("configurationStoreDownload")
 )
 
 func (e *SessionError) Error() string {

session.go

@@ -163,6 +163,14 @@ func (session *session) start() {
 		}
 	}
 
+	if err = session.credManager.ConfigurationStore.Download(session.irmaSession.Identifiers()); err != nil {
+		session.Handler.Failure(
+			session.Action,
+			&SessionError{ErrorType: ErrorConfigurationStoreDownload, Err: err},
+		)
+		return
+	}
+
 	missing := session.credManager.CheckSatisfiability(session.irmaSession.DisjunctionList())
 	if len(missing) > 0 {
 		session.Handler.UnsatisfiableRequest(session.Action, missing)