Todo List Application Tutorial

In this tutorial, you build the code for and run a single-page application (SPA) with Blockstack and Vue.js. Once the application is running, you take a tour through the applications’ Blockstack functionality. You’ll learn how it manages authentiation using a Blockstack ID and how it stores information associated with that ID using Blockstack Storage (Gaia).

Note: On macOS, Blockstack requires macOS High Sierra. 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.

If you prefer a video, you can view a video of the tutorial.

Before you begin

The application you build is a Vue.js application that is completely decentralized and server-less. While not strictly required to follow along, basic familiarity with Vue.js is helpful. When complete, the app is capable of the following:

  • authenticating users using Blockstack
  • posting new statuses
  • displaying statuses in the user profile
  • looking up the profiles and statuses of other users

For this tutorial, you will use the following tools:

  • your workstation’s command line
  • git to clone the tutorial code
  • npm to manage dependencies and scripts

The basic identity and storage services are provided by blockstack.js. To test the application, you need to have already registered a Blockstack ID.

Verify you have git installed

This tutorial uses git to clone the tutorial code. Verify you have installed git using the which command to verify.

$ which git
/usr/local/bin/npm

Verify you have npm installed

The tutorial relies on the npm dependency manager. Before you begin, verify you have installed npm using the which command to verify.

$ which npm
/usr/local/bin/npm

If you don’t find npm in your system, install it.

Make sure you have a Blockstack ID

Finally, make sure you have created at least one Blockstack ID. You’ll use this ID to interact with the application.

Task 1: Install the code and retrieve the dependencies

You can clone the source code with git or download and unzip the code from the repository. These instructions assume you are cloning.

  1. Install the code by cloning it.

     $ git clone https://github.com/blockstack/blockstack-todos
    
  2. Change to directory to the root of the code.

     $ cd blockstack-todos
    
  3. Use npm to install the dependencies.

     $ npm install
    

The Todo application has a basic Vue.js structure. There are several configuration files but the central programming files are in the src directory:

File Description
main.js Application initialization.
App.vue Code for handling the authResponse.
components/Landing.vue Code for the initial sign on page.
components/Dashboard.vue Application data storage and user sign out.

Task 2: Sign into the application

The example application runs in a node server on your local host. In the this section, you start the application and interact with it.

  1. Make sure you are in the root of the code base.

     $ pwd 
     /Users/moxiegirl/repos/blockstack-todos
    

    This path will be different for you, but double-check the last part to ensure that you’re in the directory into which you cloned and in which you ran npm install.

  2. Start the application in your local environment.

     $ npm run serve
    

    You should see output similar to the following:

      98% after emitting CopyPlugin                                                s   
      DONE  Compiled successfully in 5854ms                                7:34:28 PM
    
       App running at:
       - Local:   http://localhost:8080/ 
       - Network: http://192.168.0.12:8080/
    
       Note that the development build is not optimized.
     To create a production build, run npm run build.
    
  3. Open your local browser to the http://localhost:8080 URL.

    You should see a simple application:

  4. Choose Sign In with Blockstack.

    If you have already signed into Blockstack the application prompts you to select the ID to use. If you aren’t signed in, Blockstack prompts you to:

    If the login to the application is successful, the user is presented with the application:

Task 3: Learn about the sign in process

For an application developer, the application flow is similar to the typical client-server flow used by centralized sign in services (e.g., OAuth). However, with Blockstack, the authentication flow happens entirely client-side.

A decentralized application (DApp) and the Blockstack Browser communicate during the authentication flow by passing back and forth two tokens. The requesting application sends the Blockstack Browser an authRequest token. Once a user approves a sign-in, the Blockstack Browser responds to the application with an authResponse token. These tokens are JSON Web Tokens, and they are passed via URL query strings.

When a user chooses to Sign in with Blockstack on a DApp, it calls the redirectToSignIn() method which sends an authRequest to the Blockstack Browser. Blockstack passes the token in via a URL query string in the authRequest parameter:

https://browser.blockstack.org/auth?authRequest=j902120cn829n1jnvoa...

When the Blockstack Browser receives the request, it generates an (authResponse) token to the application using an ephemeral transit key . The ephemeral transit key is just used for the particular instance of the application, in this case, to sign the authRequest. The application stores the ephemeral transit key during the request generation. The public portion of the transit key is passed in the authRequest token. The Blockstack Browser uses the public portion of the key to encrypt an app-private key which is returned via the authResponse.

During sign in, the Blockstack Browser generates the app-private key from the user’s identity-address private key and the application’s appDomain. The app private key serves three functions:

  • It is used to create the credentials that give an app access to the Gaia storage bucket for that specific app.
  • It is used in the end-to-end encryption of files stored for the app in the user’s Gaia storage.
  • It serves as a cryptographic secret that apps can use to perform other cryptographic functions.

Finally, the app private key is deterministic, meaning that for a given user ID and domain name, the same private key is generated each time.

Task 4: Decode the authRequest

To decode the token and see what information it holds:

  1. Copy the authRequest string from the URL.

  2. Navigate to jwt.io.
  3. Paste the full token there.

    The output should look similar to below:

     {
       "jti": "f65f02db-9f42-4523-bfa9-8034d8edf459",
       "iat": 1555641911,
       "exp": 1555645511,
       "iss": "did:btc-addr:1ANL7TNdT7TTcjVnrvauP7Mq3tjcb8TsUX",
       "public_keys": [
         "02f08d5541bf611ded745cc15db08f4447bfa55a55a2dd555648a1de9759aea5f9"
       ],
       "domain_name": "http://localhost:8080",
       "manifest_uri": "http://localhost:8080/manifest.json",
       "redirect_uri": "http://localhost:8080",
       "version": "1.3.1",
       "do_not_include_profile": true,
       "supports_hub_url": true,
       "scopes": [
         "store_write",
         "publish_data"
       ]
     }
    

    The iss property is a decentralized identifier or did. This identifies the user and the user name to the application. The specific did is a btc-addr.

Task 5: Under the covers in the sign in code

Now, go to the underlying blockstack-todo code you cloned or downloaded. Sign in and sign out is handled in each of these files:

File Description
App.vue Handles the authResponse.
Landing.vue Generates the authRequest.
Dashboard.vue Handles sign out.

The src/components/Landing.vue code configures an AppConfig object and then uses this to create a UserSession. Then, the application calls a redirectToSignIn() function which generates the authRequest and redirects the user to the Blockstack authenticator:

    signIn () {
      const appConfig = new this.blockstack.AppConfig(['store_write', 'publish_data'])
      const UserSession = new this.blockstack.UserSession({ appConfig: appConfig })
      UserSession.redirectToSignIn()
    }

Once the user authenticates, the application handles the authResponse in the src/App.vue file. :

  mounted () {
    const UserSession = this.UserSession
    if (UserSession.isUserSignedIn()) {
      this.userData = UserSession.loadUserData()
      this.user = new this.blockstack.Person(this.userData.profile)
      this.user.username = this.userData.username
    } else if (UserSession.isSignInPending()) {
      UserSession.handlePendingSignIn()
        .then((userData) => {
          window.location = window.location.origin
        })
    }
  },

If blockstack.isUserSignedIn() is true, the user was previously signed in so Blockstack pulls the data from the browser and uses it in our application. If the check on blockstack.UserSession.isSignInPending() is true, a previous authResponse was sent to the application but hasn’t been processed yet. The handlePendingSignIn() function processes any pending sign in.

Signout is handled in src/components/Dashboard.vue.

  signOut () {
    this.UserSession.signUserOut(window.location.href)
  }

The method allows the application creator to decide where to redirect the user upon Sign Out:

Task 6: Work with the application

Now, trying adding a few items to the todo list. For example, try making a list of applications you want to see built on top of Blockstack:

Each list is immediately stored in the Gaia Hub linked to your Blockstack ID. For more information about the Gaia hub, see the overview in this documentation. You can fetch the todos.json file you just added by opening the Javascript console and running the following command:

userSession.getFile("todos.json", { decrypt: true }).then((file) => {console.log(file)})

You should see a JSON with the todos you just added:

[
  {
    "id":2,
    "text":"Software package manager secured by the blockchain",
    "completed":false
  },
  {
    "id":1,
    "text":"Mutable torrents with human readable names",
    "completed":false
  },
  {
    "id":0,
    "text":"Decentralized twitter",
    "completed":false
  }
]

Add another todo and check it off. When you fetch the newly generated file using the Javascript console, the results reflect your change. Look for "completed":true:

[
  {
    "id":3,
    "text":"Blockstack Todo",
    "completed":true
  },
  {
    "id":2,
    "text":"Software package manager secured by the blockchain",
    "completed":false
  },
 ...
]

Now that you have seen the application in action, dig into how it works.

Task 7: Implement storage

Go to the underlying blockstack-todo code you cloned or downloaded. The application interactions with your Gaia Hub originate in the src/components/Dashboard.vue file. First, examine where the changes to the Todos are processed:

watch: {
    todos: {
      handler: function (todos) {
        const UserSession = this.UserSession

        // encryption is now enabled by default
        return UserSession.putFile(STORAGE_FILE, JSON.stringify(todos))
      },
      deep: true
    }
  },

The todos JSON object is passed in and the blockstack.UserSession.putFile() method to store it in a Gaia Hub.

The code needs to read the Todo items from the storage with the blockstack.UserSession.getFile() method which returns a promise:

fetchData () {
      const UserSession = this.UserSession
      UserSession.getFile(STORAGE_FILE) // decryption is enabled by default
        .then((todosText) => {
          var todos = JSON.parse(todosText || '[]')
          todos.forEach(function (todo, index) {
            todo.id = index
          })
          this.uidCount = todos.length
          this.todos = todos
        })
},

The todos data is retrieved from the promise.

Summary

You now have everything you need to construct complex applications complete with authentication and storage on the Decentralized Internet. Why not try coding a sample application that accesses multiple profiles.

If you would like to explore the Blockstack APIs, you can visit the Blockstack Core API documentation or the Blockstack JS API.

Go forth and build!