HttpResources service should support POST method

[mshustov]

Blocks #27156 and #69506
HttpRespurces plugin supports the GET method only. I can see a couple of options here:

• add explicit method declaration (as it is in router)

httpResources.get({
  path: '/login',
  validate: {
    params: schema.object({ id: schema.string() }),
  },
},
async (context, request, response) => {
  //..
  return response.renderCoreApp();
});

• expose render API via contract

// http route handler
async (context, request, response) => {
  const body = coreStart.httpResources.asScoped(request).renderHtml(..);
  return response.ok({ body } );
});

It would allow us to support cases when a plugin renders an HTML page outside of the request context:

kibana/x-pack/plugins/security/server/authorization/authorization_service.tsx

Lines 168 to 198 in e31ec7e

	http.registerOnPreResponse((request, preResponse, toolkit) => {
	if (preResponse.statusCode === 403 && canRedirectRequest(request)) {
	const basePath = http.basePath.get(request);
	const next = `${basePath}${request.url.path}`;
	const regularBundlePath = `${basePath}/${buildNumber}/bundles`;
	const logoutUrl = http.basePath.prepend(
	`/api/security/logout?${querystring.stringify({ next })}`
	);
	const styleSheetPaths = [
	`${regularBundlePath}/kbn-ui-shared-deps/${UiSharedDeps.baseCssDistFilename}`,
	`${regularBundlePath}/kbn-ui-shared-deps/${UiSharedDeps.lightCssDistFilename}`,
	`${basePath}/node_modules/@kbn/ui-framework/dist/kui_light.css`,
	`${basePath}/ui/legacy_light_theme.css`,
	];
	const body = renderToStaticMarkup(
	<ResetSessionPage
	logoutUrl={logoutUrl}
	styleSheetPaths={styleSheetPaths}
	basePath={basePath}
	/>
	);
	return toolkit.render({ body, headers: { 'Content-Security-Policy': http.csp.header } });
	}
	return toolkit.next();
	});
	return authz;
	}

That's why I'm inclining towards this option.

@elastic/kibana-platform WDYT?

[pgayvallet]

+1 for option 2. Even if diverging from the http API, it feels more extensible and allowing to use it outside of request context seems just too important.

[mshustov]

@elastic/kibana-security let us know when you need this implemented

[legrego]

@azasypkin can keep me honest, but I don't think this is blocking anything critical. This is something we'd really like to have, but I'm not aware of any deadlines that we need to hit.

In other words, I wouldn't reprioritize your current work, but otherwise we'd love to have this as soon as you get some free time.