in saml-authentication-server/src/main/java/jetbrains/buildServer/auth/saml/plugin/SamlAuthenticationScheme.java [327:332]
private HttpAuthenticationResult sendUnauthorizedRequest(HttpServletRequest request, HttpServletResponse response, String reason) throws IOException {
LOG.warn(reason);
HttpAuthUtil.setUnauthenticatedReason(request, reason);
response.sendError(HttpStatus.UNAUTHORIZED.value(), reason);
return HttpAuthenticationResult.unauthenticated();
}