Add GitHub OAuth App to example (#193)

example/README.md

@@ -2,20 +2,28 @@
 
 This is an example application using oauth2cli.
 
+To build this application,
 
-## Getting Started
+```sh
+go build
+```
 
-Setup your Google API access:
+## Google
+
+Create your OAuth client.
 
 1. Open https://console.cloud.google.com/apis/credentials
 1. Create an OAuth client ID where the application type is other.
 
-Build and run the application:
+Run this application.
 
+```sh
+./example -client-id xxx.apps.googleusercontent.com -client-secret xxxxxxxx
 ```
-% go build
-% ./example -client-id xxx.apps.googleusercontent.com -client-secret xxxxxxxx
+
+```console
 2019/10/03 00:01:35 Open http://localhost:53753
+...
 2019/10/03 00:01:40 You got a valid token until 2019-10-03 01:01:40.083238 +0900 JST m=+3604.526750517
 ```
 
@@ -29,3 +37,25 @@ You can set a certificate and key for the local server.
 ./example -client-id xxx.apps.googleusercontent.com -client-secret xxxxxxxx \
   -local-server-cert ../e2e_test/testdata/cert.pem -local-server-key ../e2e_test/testdata/cert-key.pem
 ```
+
+## GitHub
+
+Create your OAuth App.
+Set the callback URL to `http://localhost`.
+
+Run this application.
+
+```sh
+./example -auth-url https://github.com/login/oauth/authorize -token-url https://github.com/login/oauth/access_token -client-id xxxxxxxx -client-secret xxxxxxxx
+```
+
+```console
+09:52:45.384489 main.go:84: Open http://localhost:61865
+09:52:45.384507 server.go:36: oauth2cli: starting a server at 127.0.0.1:61865
+09:52:45.491072 server.go:135: oauth2cli: sending redirect to https://github.com/login/oauth/authorize?client_id=...
+```
+
+You can set `-scopes` flag to request the scopes.
+See https://docs.github.com/en/apps/oauth-apps/building-oauth-apps/scopes-for-oauth-apps.
+
+It will automatically open the browser and you can log in to GitHub.