hansenjl/sinatra-password-security-onl01-seng-ft-050420

Securing Passwords

Objectives

1. Learn about bcrypt, a gem that works to encrypt passwords.
2. Learn about Active Record's has_secure_password method.
3. Sign up and log in a user with a secure, encrypted password.

Overview

Securing users' data is one of the most important jobs of a web developer. Despite frequent warnings against it, many of your users will use the same username and password combination across many different websites. This means that, in general, people will use the same password for our applications that they do for their bank.

Because of this, we never want to store our users' passwords in plain text in our database. Instead, we'll run the passwords through a hashing algorithm. A hashing algorithm manipulates data in such a way that it cannot be un-manipulated. This is to say that if someone got a hold of the hashed version of a password, they would have no way to turn it back into the original. In addition to hashing the password, we'll also add a "salt". A salt is simply a random string of characters that gets added into the hash. That way, if two of our users use the password "fido", they will end up with different hashes in our database.

We'll use an open-source gem, bcrypt, to implement this strategy.

Starter Code

We've got a basic Sinatra MVC application. In our application_controller we have two helper methods defined: logged_in? returns true or false based on the presence of a session[:user_id], and current_user returns the instance of the logged in user, based on the session[:user_id]. We have six actions defined:

• get "/" renders an index.erb file with links to signup or login.
• get '/signup' renders a form to create a new user. The form includes fields for username and password.
• get '/login' renders a form for logging in.
• get '/success' renders a success.erb page, which should be displayed once a user successfully logs in.
• get '/failure' renders a failure.erb page. This will be accessed if there is an error logging in or signing up.
• get '/logout' clears the session data and redirects to the homepage.

We've also stubbed out a user model in app/models/user.rb that inherits from ActiveRecord::Base.

Fork and clone this repository and run bundle install to get started!

Password Encryption with BCrypt

BCrypt will store a salted, hashed version of our users' passwords in our database in a column called password_digest. Essentially, once a password is salted and hashed, there is no way for anyone to decode it. This method requires that hackers use a 'brute force' approach to gain access to someone's account –– still possible, but more difficult.

Implementing BCrypt

We've created a migration file for you, but you'll need to fill it in. For now, we'll use def up and def down methods for this lab, but note that you will often see def change now when generating migrations. Let's edit that file so that it actually creates a users table. We'll have two columns: one for username and one for password_digest.

class CreateUsers < ActiveRecord::Migration[5.1]
  def up
    create_table :users do |t|
      t.string :username
      t.string :password_digest
    end
  end

  def down
    drop_table :users
  end
end

Run this migration using rake db:migrate. Preview your work by running shotgun and navigating to localhost:9393 in your browser. Awesome job!

NOTE: If you're in the Learn IDE, instead of going to localhost:9393 you'll navigate to the URL output by the shotgun command.

ActiveRecord's has_secure_password

Next, let's update our user model so that it includes has_secure_password. This ActiveRecord macro gives us access to a few new methods. A macro is a method that when called, creates methods for you. This is meta programming, which you don't need to worry about now. Just know that using a macro is just like calling a normal ruby method.

In this case, the macro has_secure_password is being called just like a normal ruby method. It works in conjunction with a gem called bcrypt and gives us all of those abilities in a secure way that doesn't actually store the plain text password in the database.

class User < ActiveRecord::Base
  has_secure_password
end

Next, let's handle signing up. In our post '/signup' action, let's make a new instance of our user class with a username and password from params. Note that even though our database has a column called password_digest, we still access the attribute of password. This is given to us by has_secure_password. You can read more about that in the Ruby Docs.

post "/signup" do
  user = User.new(:username => params[:username], :password => params[:password])
end

Because our user has has_secure_password, we won't be able to save this to the database unless our user filled out the password field. Calling user.save will return false if the user can't be persisted. Let's update this route so that we redirect to '/login' if the user is saved, or '/failure' if the user can't be saved. (For now, we'll make the user log in after they sign up successfully).

post "/signup" do
  user = User.new(:username => params[:username], :password => params[:password])

  if user.save
    redirect "/login"
  else
    redirect "/failure"
  end
end

Awesome! Test this feature out in your browser. Leaving the password field blank should land you at the "failure" page, while creating a valid user should take you to login.

Next, create at least one valid user, then let's build out our login action. In post '/login', let's find the user by username.

post "/login" do
  user = User.find_by(:username => params[:username])
end

Next, we need to check two conditions: first, did we find a user with that username? This can be written as user != nil or simply user.

post "/login" do
  user = User.find_by(:username => params[:username])
  if user
    redirect "/success"
  else
    redirect "/failure"
  end
end

We also need to check if that user's password matches up with the value in password_digest. Users must have both an account and know the password.

We validate password match by using a method called authenticate on our User model. We do not have to write this method ourselves. Rather when we added the line of code to User:

class User < ActiveRecord::Base
  has_secure_password
end

we told Ruby to add an authenticate method to our class (invisibly!) when the program runs. While we, as programmers can't see it, it will be there.

ASIDE This is one of the special powers of Ruby called "metaprogramming:" writing code that writes code. Ruby code can run methods on itself so that classes gain new methods or state when the code runs! Pretty cool! Ruby and only a few other languages have this ability.

Using metaprogramming is controversial, though. On the one hand, it can save developers time. On the other, and we see that in this lesson, it would be nice to point to where on some line, in some file, the authenticate method was defined. Reasonable developers can have differences of opinion as to whether to use metaprogramming. Understanding metaprogramming perfectly is not essential to being a Ruby or Rails developer.

Let's step through the process of how User's authenticate method works. It:

1. Takes a String as an argument e.g. i_luv@byron_poodle_darling
2. It turns the String into a salted, hashed version (76776516e058d2bf187213df6917a7e)
3. It compares this salted, hashed version with the user's stored salted, hashed password in the database
4. If the two versions match, authenticate will return the User instance; if not, it returns false

IMPORTANT At no point do we look at an unencrypted version of the user's password.

In the code below, we see how we can ensure that we have a User AND that that User is authenticated. If the user authenticates, we'll set the session[:user_id] and redirect to the /success route. Otherwise, we'll redirect to the /failure route so our user can try again.

post "/login" do
  user = User.find_by(:username => params[:username])

  if user && user.authenticate(params[:password])
    session[:user_id] = user.id
    redirect "/success"
  else
    redirect "/failure"
  end
end

Awesome job! We've now built out a basic authentication system for a user without storing a plain-text password in our database.

Video Review

• Authentication

Resources

• BCrypt Ruby
• Intro to BCrypt & Password Security - MakerSquare on YouTube
• Ruby on Rails Guide: Has Secure Password
• How NOT to Store Passwords! - Computerphile on Youtube

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