feat(backend): allow services to provide whoami values

packages/backend/src/CoreModule.js

@@ -219,6 +219,9 @@ const install = async ({ services, app }) => {
 
     const { GetUserService } = require('./services/GetUserService');
     services.registerService('get-user', GetUserService);
+
+    const { DetailProviderService } = require('./services/DetailProviderService');
+    services.registerService('whoami', DetailProviderService);
 }
 
 const install_legacy = async ({ services }) => {

packages/backend/src/routers/whoami.js

@@ -60,6 +60,11 @@ const WHOAMI_GET = eggspress('/whoami', {
         ...(req.new_token ? { token: req.token } : {})
     };
 
+    // Get whoami values from other services
+    const svc_whoami = req.services.get('whoami');
+    const provider_details = await svc_whoami.get_details({ user: req.user });
+    Object.assign(details, provider_details);
+
     if ( ! is_user ) {
         // When apps call /whoami they should not see these attributes
         // delete details.username;

packages/backend/src/services/DetailProviderService.js

@@ -0,0 +1,29 @@
+const BaseService = require("./BaseService")
+
+/**
+ * A generic service class for any service that enables registering
+ * detail providers. A detail provider is a function that takes an
+ * input object and uses its values to populate another object.
+ */
+class DetailProviderService extends BaseService {
+    _construct () {
+        this.providers_ = [];
+    }
+
+    register_provider (fn) {
+        this.providers_.push(fn);
+    }
+
+    async get_details (context) {
+        const details = {};
+
+        for (const provider of this.providers_) {
+            const out = await provider(context);
+            Object.assign(details, out);
+        }
+
+        return details;
+    }
+}
+
+module.exports = { DetailProviderService }