In previous post we saw how to buil RESTful API using Grape. In this post we will see how to add devise auth token to users and how to use it in Grape API authentication.

Lets see how this can be done assuming you already have devise setup ready.
## Add token_authenticable to devise modules (works with devise versions <=3.2)
In user.rb add :token_authenticatable to the list of devise modules, it should look something like below:

## Generate Authentication token on your own (If devise version > 3.2)

Add migration for authentiction token

rails g migration add_auth_token_to_users
      invoke  active_record
      create    db/migrate/20140326204628_add_auth_token_to_users.rb

Edit migration file to add :authentication_token column to users

Run migrations

rake db:migrate

Generate token for existing users

We need to call save on every instance of user that will ensure authentication token is present for each user.

Secure Grape API using auth token

You need to add below code to the API::Root in-order to add token based authentication. If you are unware of API::Root then please read Building RESTful API using Grape

In below example, We are authenticating user based on two scenarios
- If user is logged on to the web app then use the same session
- If session is not available and auth token is passed then find user based on the token