Assuming you have the project setup ready if not, see my post Getting started with Karate Automation . Once your project is set let’s start with creating a folder structure in Eclipse.
The below project is the maven project and src/test/java have a package called authentication which will have all authentication related feature files.

After you have created your authentication package you can create a feature file inside the same package and name it “Authentication.feature“.
Now add the below code into the feature file which will help you authentication a user using grant type implicit.

Feature: Implicit Auth

* url authURL

Scenario: Verify the user details using OAuth2 Implicit grant type

* path 'token'
* form field grant_type = 'password'
* form field username = 'username'
* form field password = 'password'
* form field client_id = 'appId'
* form field client_secret = 'appSecret'
* form field scope = 'your_App_Scope'
* method post
* status 200
* print response
* def accessToken = response.access_token
* header Authorization = 'Bearer ' + token

Once you have you Authentication set, create another scenario to create a test if the Authentication is working

Scenario: get all employer details
* path 'YourAPPURL'
Given def query = read('yourRequestFileName.json')
#Change your data as below
And def variables = { name: 'Charmander' }
And request { query: '#(query)', variables: '#(variables)' }
#And request { query: '#(query)' } 
When method post
* print response
Then status 200