Add a login command

src/commands/login.ts

+import { Command, flags } from '@oclif/command';
+import chalk from 'chalk';
+import cli from 'cli-ux';
+import * as inquirer from 'inquirer';
+
+import { CloudAuth } from '../misc/cloudAuth';
+
+export default class Login extends Command {
+    public static description = 'steps through the process to log in with Rocket.Chat Cloud';
+
+    public static flags = {
+        help: flags.help({ char: 'h' }),
+    };
+
+    public async run() {
+        inquirer.registerPrompt('checkbox-plus', require('inquirer-checkbox-plus-prompt'));
+
+        const cloudAuth = new CloudAuth();
+        const hasToken = await cloudAuth.hasToken();
+        if (hasToken) {
+            await cloudAuth.getToken();
+            cli.log(chalk.green('you are already logged in!'));
+        } else {
+            try {
+                cli.log(chalk.green('*') + ' ' + chalk.gray('waiting for authorization...'));
+                await cloudAuth.executeAuthFlow();
+                cli.action.stop('success!');
+            } catch (e) {
+                cli.action.stop('failure to authenticate.');
+                return;
+            }
+        }
+    }
+}