chore: add Github example (#175)

* feat: add Github example

* refactor: use `getAccessTokenFromRefreshToken` instead of API request

#174 (comment)

Author: frixaco

examples/github.js

@@ -0,0 +1,92 @@
+'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: 'githubOAuth2',
+  scope: [],
+  credentials: {
+    client: {
+      id: '<CLIENT_ID>',
+      secret: '<CLIENT_SECRET>'
+    },
+    auth: oauthPlugin.GITHUB_CONFIGURATION
+  },
+  startRedirectPath: '/login/github',
+  callbackUri: 'http://localhost:3000/login/github/callback'
+})
+
+const memStore = new Map()
+
+async function saveAccessToken (token) {
+  memStore.set(token.refresh_token, token)
+}
+
+async function retrieveAccessToken (token) {
+  // remove Bearer if needed
+  if (token.startsWith('Bearer ')) {
+    token = token.substring(6)
+  }
+  // any database or in-memory operation here
+  // we use in-memory variable here
+  if (memStore.has(token)) {
+    memStore.get(token)
+  }
+  throw new Error('invalid refresh token')
+}
+
+fastify.get('/login/github/callback', async function (request, reply) {
+  const token = await this.githubOAuth2.getAccessTokenFromAuthorizationCodeFlow(request)
+
+  console.log(token.access_token)
+
+  // you should store the `token` for further usage
+  await saveAccessToken(token)
+
+  reply.send({ access_token: token.access_token })
+})
+
+fastify.get('/login/github/refreshAccessToken', async function (request, reply) {
+  // we assume the token is passed by authorization header
+  const refreshToken = await retrieveAccessToken(request.headers.authorization)
+  const newToken = await this.githubOAuth2.getAccessTokenFromRefreshToken(refreshToken, {})
+
+  // we save the token again
+  await saveAccessToken(newToken)
+
+  reply.send({ access_token: newToken.access_token })
+})
+
+// Check access token: https://docs.github.com/en/rest/apps/oauth-applications#check-a-token
+fastify.get('/login/github/verifyAccessToken', function (request, reply) {
+  const { accessToken } = request.query
+
+  sget.concat(
+    {
+      url: 'https://api.github.com/applications/<CLIENT_ID>/token',
+      method: 'POST',
+      headers: {
+        Authorization:
+          'Basic ' +
+          Buffer.from('<CLIENT_ID>' + ':' + '<CLIENT_SECRET').toString(
+            'base64'
+          )
+      },
+      body: JSON.stringify({ access_token: accessToken }),
+      json: true
+    },
+    function (err, res, data) {
+      if (err) {
+        reply.send(err)
+        return
+      }
+      reply.send(data)
+    }
+  )
+})
+
+fastify.listen({ port: 3000 })