In this tutorial, you build on the <ahref="{{ site.baseurl }}/browser/hello-blockstack.html"target="\_blank">Hello, Blockstack Tutorial</a>. You'll modify the authentication code so that it prompts users who have not yet created a Blockstack identity, to choose a hub URL.
* TOC
{:toc}
{% include note.html content="This tutorial was written on macOS High Sierra 10.13.4. If you use a Windows or Linux system, you can still follow along. However, you will need to \"translate\" appropriately for your operating system. Additionally, this tutorial assumes you are accessing the Blockstack Browser web application via Chrome. The application you build will also work with a local installation and/or with browsers other than Chrome. " %}
## About this tutorial and the prerequisites you need
This tutorial assumes you already set up your environment and tooling as specified in the <ahref="{{ site.baseurl }}/browser/hello-blockstack.html"target="\_blank">Hello, Blockstack Tutorial</a>. You should also review that tutorial for basic information about
## Task 1: Generate an initial Blockstack application
In this section, you build an initial React.js application called `hello-hub-choice`.
1. Create the `hello-hub-choice` directory.
```bash
mkdir hello-hub-choice
```
2. Change into your new directory.
```bash
cd hello-hub-choice
```
3. Use Yeoman and the Blockstack application generator to create your initial `hello-hub-choice` application.
```bash
yo blockstack
```
You should see several interactive prompts.
{% raw %}
```bash
$ yo blockstack
...
? Are you ready to build a Blockstack app in React? (Y/n)
```
{% endraw %}
4. Respond to the prompts to populate the initial app.
After the process completes successfully, you see a prompt similar to the following:
{% raw %}
```bash
...
create public/icon-192x192.png
create public/index.html
create public/robots.txt
create public/manifest.json
Im all done. Running npm install for you to install the required dependencies. If this fails, try running the command yourself.
```
{% endraw %}
5. Verify that you have version `18.3.0` of blockstack.js or higher.
If you don't have the correct version, install it.
```
npm install blockstack@18.3.0
```
Depending on your environment you may have some problems with the `npm` packages. Go ahead and fix these before continuing to the next section.
## Task 2. Start the server and view the application
When you start the server, it will create a Node.js server, start it locally,
and open your browser `http://localhost:5000`. From the root of your new application directory:
1. Start the application server.
```bash
npm start
```
2. Choose **Allow**.
3. Open your browser to `http://localhost:8080`.
You should see a simple application:
4. Leave your new application running and move onto the next section.
## Task 3: Enable hub selection
By default, the app generator assumes you want to use the default flow `redirectToSignIn()` method. In this section, you replace that method and use the `makeAuthRequest()` method instead. The `makeAuthRequest()` method takes the following parameters:
<dd>The time at which this request is no longer valid.</dd>
<dtclass="uk-text-lowercase">
<code>extraParams(Object = {})</code>
</dt>
<dd>Any extra parameters to pass to the authenticator. Use this to pass options that aren't part of the Blockstack authentication specification, but might be supported by special authenticators.</dd>
</dl>
To replace the default login, do the following:
1. Using your favorite editor, open the `public/app.js` file.
2. Locate the `redirectToSignIn()` method at line 4.
