Support plugin-specific route options validation

[jonathansamines]

Support plan

• which support plan is this issue covered by? (e.g. Community, Core, Plus, or Enterprise): Community
• is this issue currently blocking your project? (yes/no): No
• is this issue affecting a production system? (yes/no): No

Context

• node version: 12 LTS
• module version: 19.1.1
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): hapi application
• any other relevant information: none

What problem are you trying to solve?

When authoring a plugin that can be configured "per route", it is often necessary to validate those options (ideally at boot time) so that no incorrect configuration is provided to the plugin.

server.route({
    method: 'GET',
    path: '/',
    options: {
        plugins: {
            pluginNS: {} // validate these options are correct at boot time
        }
    }   
});

It is possible to manually perform this validation, but ideally a more declarative approach can be used.

Validating at boot time:

server.ext('onPreStart', () => {

        // Prepare plugin options

        const routes = server.table();
        for (const route of routes) {
            if ('pluginNS' in route.settings.plugins) {
                route.settings.plugins.pluginNS = Joi.attempt(route.settings.plugins.pluginNS, schema);
            }
        }
    });

Reference: https://github.com/kanongil/nipo/blob/master/lib/index.js#L404-L414

Validating at runtime:

options = Joi.attempt(request.route.settings.plugins.pluginNS, schema);

Reference: https://github.com/nlf/blankie/blob/master/lib/index.js#L271

Do you have a new or modified API suggestion to solve the problem?

I don't have a particular approach or design in mind. Any help here would be appreciated.