Implement owner service create() method for registering an owner

(Registering means saving their non-secret key information.)

server/globals.js

@@ -30,4 +30,8 @@ module.exports = function (app) {
   app.set('serverSecretFileExists', serverSecretFileExists)
   app.set('ownerKeysFileExists', ownerKeysFileExists)
   app.set('ownerSettingsFileExists', ownerSettingsFileExists)
+
+  // Aliases
+
+  app.set('ownerExists', ownerKeysFileExists)
 }

server/services/owner/owner.class.js

+const errors = require('@feathersjs/errors')
+const fs = require('fs-extra')
+
 /* eslint-disable no-unused-vars */
 class Service {
   constructor (options) {
-    this.options = options || {};
+    this.options = options || {}
+  }
+
+  // This method is required to be able to pass the feathers app object.
+  setup (app, appPath) {
+    this.app = app
   }
 
   async find (params) {
-    return [];
+    return []
   }
 
   async get (id, params) {
     return {
       id, text: `A new message with ID: ${id}!`
-    };
+    }
   }
 
+  // Registers a new owner.
   async create (data, params) {
-    if (Array.isArray(data)) {
-      return await Promise.all(data.map(current => this.create(current)));
+    // TODO: Do not use sync method
+    if (this.app.get('ownerExists')) {
+      const error = new errors.Forbidden('Owner already exists.')
+      throw error
     }
 
-    return data;
+    const ownerKeysFilePath = this.app.get('ownerKeysFilePath')
+
+    const ownerKeysObject = {
+      derivedKeySalt: data.derivedKeySalt,
+      encryptedPrivateSigningKeyNonce: data.encryptedPrivateSigningKeyNonce,
+      encryptedPrivateSigningKey: data.encryptedPrivateSigningKey,
+      publicSigningKey: data.publicSigningKey
+    }
+
+    try {
+      await fs.writeJson(ownerKeysFilePath, ownerKeysObject, {spaces: 2})
+      return data
+    } catch (error) {
+      throw new errors.GeneralError('Failed to save owner’s keys.', error)
+    }
   }
 
   async update (id, data, params) {
-    return data;
+    return data
   }
 
   async patch (id, data, params) {
-    return data;
+    return data
   }
 
   async remove (id, params) {
-    return { id };
+    return { id }
   }
 }
 
 module.exports = function (options) {
-  return new Service(options);
-};
+  return new Service(options)
+}
 
-module.exports.Service = Service;
+module.exports.Service = Service