Use LinkedIn Sign In with Firebase and also with nodejs

This sample shows how to authenticate using LinkedIn Sign-In on Firebase. In this sample we use OAuth 2.0 based authentication to get LinkedIn user information then create a Firebase Custom Token (using the LinkedIn user ID).

Setup the sample

Create and setup the Firebase project:

1. Create a Firebase project using the Firebase Developer Console.
2. Enable Billing on your Firebase the project by switching to the Blaze plan, this is currently needed to be able to perform HTTP requests to external services from a Cloud Function.

Create and provide a Service Account's credentials:

1. Create a Service Accounts file as described in the Server SDK setup instructions.
2. Save the Service Account credential file as ./functions/service-account.json

Create and setup your LinkedIn app:

1. Create a LinkedIn app in the LinkedIn Developers website.

2. Add the URL https://<application-id>.firebaseapp.com/popup.html to the OAuth 2.0 > Authorized Redirect URLs of your LinkedIn app.

3. Copy the Client ID and Client Secret of your LinkedIn app and use them to set the linkedin.client_id and linkedin.client_secret Google Cloud environment variables. For this use:

   firebase functions:config:set linkedin.client_id="yourClientID" linkedin.client_secret="yourClientSecret"

Make sure the LinkedIn Client Secret is always kept secret. For instance do not save this in your version control system.

Deploy your project:

1. Run firebase use --add and choose your Firebase project. This will configure the Firebase CLI to use the correct project locally.
2. Run firebase deploy to effectively deploy the sample. The first time the Functions are deployed the process can take several minutes.

Run the sample

step 1.
    ```bash
    npm install
    ```
    ```bash
    yarn
    ```
step 2.
    ```bash
    npm start
    ```
    ```bash
    yarn start
    ```