authcodegrant samples->oauth2webclient samples

The authcodegrant samples were initially meant to be very simple
demonstration of authorization code flow. However, it has become
obvious since then that the real intent of the demo is how to use
the WebClient with OAuth (there is no other reason to do authorization
code flow unless you use the token to make a request).

The samples have been migrated to oauth2webclient and oauth2webclient-webflux
respectively. They have been improved:

* The sample demonstrates usage with annotations, webclient directly, form login
  oauth2Login, and public APIs
* The samples externalize the endpoint that is requested in the sample
  making it easier to try other endpoints
* The UI no longer relies on a data structure for the result of the
  endpoint also making it easier to try other endpoints

Issue: gh-4921

Author: rwinch

samples/boot/authcodegrant-webflux/src/integration-test/java/sample/OAuth2AuthorizationCodeGrantApplicationTests.java

@@ -1,8 +1,8 @@
-= OAuth 2.0 Authorization Code Grant Sample
+= OAuth 2.0 WebClient (WebFlux) Sample
 
 == GitHub Repositories
 
-This guide provides instructions on setting up the sample application, which leverages the OAuth 2.0 Authorization Code Grant, and displays a list of public GitHub repositories that are accessible to the authenticated user.
+This guide provides instructions on setting up the sample application, which leverages WebClient OAuth2 integration to display a list of public GitHub repositories that are accessible to the authenticated user.
 
 This includes repositories owned by the authenticated user, repositories where the authenticated user is a collaborator, and repositories that the authenticated user has access to through an organization membership.
 
@@ -17,7 +17,7 @@ The following sections provide detailed steps for setting up the sample and cove
 
 To use GitHub's OAuth 2.0 authorization system, you must https://github.com/settings/applications/new[Register a new OAuth application].
 
-When registering the OAuth application, ensure the *Authorization callback URL* is set to `http://localhost:8080/github-repos`.
+When registering the OAuth application, ensure the *Authorization callback URL* is set to `http://localhost:8080/login/oauth2/code/client-id`.
 
 The Authorization callback URL (redirect URI) is the path in the application that the end-user's user-agent is redirected back to after they have authenticated with GitHub and have granted access to the OAuth application on the _Authorize application_ page.
 
@@ -36,12 +36,11 @@ spring:
     oauth2:
       client:
         registration:	<1>
-          github:       <2>
-            client-id: github-client-id
-            client-secret: github-client-secret
-            scope: public_repo
-            redirect-uri-template: "{baseUrl}/github-repos"
-            client-name: GitHub Repositories
+          client-id:       <2>
+            client-id: replace-with-client-id
+            client-secret: replace-with-client-secret
+            provider: github
+            scopes: read:user,public_repo
 ----
 +
 .OAuth Client properties
@@ -57,7 +56,7 @@ spring:
 
 Launch the Spring Boot 2.0 sample and go to `http://localhost:8080`.
 You are then redirected to the default _auto-generated_ form login page.
-Log in using *'user'* (username) and *'password'* (password) and then you'll be redirected to GitHub for authentication.
+Log in using *'user'* (username) and *'password'* (password) or click the link to authenticate with GitHub and then you'll be redirected to GitHub for authentication.
 
 After authenticating with your GitHub credentials, the next page presented to you is "Authorize application".
 This page will ask you to *Authorize* the application you created in the previous step.