Feature: OpenID Connect Discovery support (#242)

* feat: oidc metadata discovery implementation

* docs: adds discovery example in readme

* feat(types): add type defs and tests

* docs: better docs

* test: swap test names to match the intent

* ci: just an empty commit to trigger GA

* fix: address pkce method selection when op doesn't announce it in discovery

* test: fix tests for inconsistent JSON parse err between node versions

* feat: better handling for missing endpoints - either can be ommited

README.md

@@ -120,6 +120,43 @@ fastify.register(oauthPlugin, {
 })
 ```
 
+## Use automated discovery endpoint
+
+When your provider supports OpenID connect discovery and you want to configure authorization, token and revocation endpoints automatically, 
+then you can use discovery option.
+`discovery` is a simple object that requires `issuer` property.
+
+Issuer is expected to be string URL or metadata url.
+Variants with or without trailing slash are supported.
+
+You can see more in [example here](./examples/discovery.js).
+
+```js
+fastify.register(oauthPlugin, {
+  name: 'customOAuth2',
+  scope: ['profile', 'email'],
+  credentials: {
+    client: {
+      id: '<CLIENT_ID>',
+      secret: '<CLIENT_SECRET>',
+    },
+    // Note how "auth" is not needed anymore when discovery is used.
+  },
+  startRedirectPath: '/login',
+  callbackUri: 'http://localhost:3000/callback',
+  discovery: { issuer: 'https://identity.mycustomdomain.com' }
+  // pkce: 'S256', you can still do this explicitly, but since discovery is used,
+  // it's BEST to let plugin do it itself 
+  // based on what Authorization Server Metadata response
+});
+```
+
+Important notes for discovery:
+
+- You should not set up `credentials.auth` anymore when discovery mechanics is used.
+- When your provider supports it, plugin will also select appropriate PKCE method in authorization code grant
+- In case you still want to select method yourself, and know exactly what you are doing; you can still do it explicitly.
+
 ### Schema configuration
 
 You can specify your own schema for the `startRedirectPath` end-point. It allows you to create a well-documented document when using `@fastify/swagger` together.

examples/discovery.js

@@ -0,0 +1,89 @@
+'use strict'
+
+const fastify = require('fastify')({ logger: { level: 'trace' } })
+const sget = require('simple-get')
+
+const cookieOpts = {
+  // domain: 'localhost',
+  path: '/',
+  secure: true,
+  sameSite: 'lax',
+  httpOnly: true
+}
+
+// const oauthPlugin = require('fastify-oauth2')
+fastify.register(require('@fastify/cookie'), {
+  secret: ['my-secret'],
+  parseOptions: cookieOpts
+})
+
+const oauthPlugin = require('..')
+fastify.register(oauthPlugin, {
+  name: 'googleOAuth2',
+  // when provided, this userAgent will also be used at discovery endpoint
+  // to fully omit for whatever reason, set it to false
+  userAgent: 'my custom app (v1.0.0)',
+  scope: ['openid', 'profile', 'email'],
+  credentials: {
+    client: {
+      id: process.env.CLIENT_ID,
+      secret: process.env.CLIENT_SECRET
+    }
+  },
+  startRedirectPath: '/login/google',
+  callbackUri: 'http://localhost:3000/interaction/callback/google',
+  cookie: cookieOpts,
+  // pkce: 'S256' let discovery handle it itself
+  discovery: {
+    /*
+    When OIDC provider is mounted at root:
+    with trailing slash (99% of the cases)
+    - 'https://accounts.google.com/'
+    */
+    issuer: 'https://accounts.google.com'
+    /*
+    also these variants work:
+    When OIDC provider is mounted at root:
+    with trailing slash
+    - 'https://accounts.google.com/'
+
+    When given explicit metadata endpoint:
+    - issuer: 'https://accounts.google.com/.well-known/openid-configuration'
+
+    When OIDC provider is nested at some route:
+     - with trailing slash
+    'https://id.mycustomdomain.com/nested/'
+    - without trailing slash
+    'https://id.mycustomdomain.com/nested'
+    */
+  }
+})
+
+fastify.get('/interaction/callback/google', function (request, reply) {
+  // Note that in this example a "reply" is also passed, it's so that code verifier cookie can be cleaned before
+  // token is requested from token endpoint
+  this.googleOAuth2.getAccessTokenFromAuthorizationCodeFlow(request, reply, (err, result) => {
+    if (err) {
+      reply.send(err)
+      return
+    }
+
+    sget.concat({
+      url: 'https://www.googleapis.com/oauth2/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 })
+fastify.log.info('go to http://localhost:3000/login/google')