Add linkedin authentication example (#250)

* Add linkedin authentication example

ise tokenRequestParams to proceed with the correct flow with getAccessTokenFromAuthorizationCodeFlow

* code format running lint:fix

Author: lucafregoso

examples/linkedin.js

@@ -0,0 +1,57 @@
+'use strict'
+
+const fastify = require('fastify')({ logger: { level: 'trace' } })
+const sget = require('simple-get')
+
+// const oauthPlugin = require('fastify-oauth2')
+const oauthPlugin = require('..')
+
+fastify.register(oauthPlugin, {
+  name: 'linkedinOAuth2',
+  scope: ['profile', 'email', 'openid'],
+  credentials: {
+    client: {
+      id: '<CLIENT_ID>',
+      secret: '<CLIENT_SECRET>'
+    },
+    auth: oauthPlugin.LINKEDIN_CONFIGURATION
+  },
+  tokenRequestParams: {
+    client_id: '<CLIENT_ID>',
+    client_secret: '<CLIENT_SECRET>'
+  },
+  startRedirectPath: '/login/linkedin',
+  callbackUri: 'http://localhost:3000/login/linkedin/callback'
+})
+
+fastify.get('/login/linkedin/callback', function (request, reply) {
+  this.linkedinOAuth2.getAccessTokenFromAuthorizationCodeFlow(
+    request,
+    (err, result) => {
+      if (err) {
+        reply.send(err)
+        return
+      }
+
+      sget.concat(
+        {
+          url: 'https://api.linkedin.com/v2/userinfo',
+          method: 'GET',
+          headers: {
+            Authorization: 'Bearer ' + result.token.access_token
+          },
+          json: true
+        },
+        function (err, res, data) {
+          if (err) {
+            reply.send(err)
+            return
+          }
+          reply.send(data)
+        }
+      )
+    }
+  )
+})
+
+fastify.listen({ port: 3000 })