以github为例，简要介绍OAuth第三方登录流程。
参考：

GitHub OAuth 第三方登录示例教程

流程

github第三方登录示例 - 图1

代码

web

  1. <!DOCTYPE html>
  2. <html>
  4. <head>
  5.     <meta charset="utf-8"/>
  6.     <meta http-equiv="X-UA-Compatible" content="IE=edge">
  7.     <title>Node OAuth2 Demo</title>
  8.     <meta name="viewport" content="width=device-width, initial-scale=1">
  9. </head>
  11. <body>
  12. <a id="login">Login with GitHub</a>
  14. <script>
  15.     // fill in your cliend_id
  16.     const client_id = '2d6ab4268ae36f01a7a4';
  18.     const authorize_uri = 'https://github.com/login/oauth/authorize';
  19.     const redirect_uri = 'http://localhost:8080/oauth/redirect';
  21.     const link = document.getElementById('login');
  22.     link.href = `${authorize_uri}?client_id=${client_id}&redirect_uri=${redirect_uri}`;
  23. </script>
  25. </body>
  27. </html>

本地接口

  1. /**
  2.  * @Description
  3.  * @Author 田云
  4.  * @Date 2019/6/4 16:17
  5.  * @Version 1.0
  6.  */
  7. @RestController
  8. @RequestMapping("oauth")
  9. public class Login {
  11.     private String client_id = "XXX";
  12.     private String client_secret = "XXX";
  14.     @GetMapping("redirect")
  15.     public String login(String code) {
  16.         String me = CommonUtil.sendPost
  17.                 ("https://github.com/login/oauth/access_token?" +
  18.                                 "client_id=" + client_id +
  19.                                 "&client_secret=" + client_secret +
  20.                                 "&code=" + code,
  21.                         null);
  23.         String atoke = me.split("&")[0];
  25.         String res = CommonUtil.sendGet("https://api.github.com/user?" + atoke + "");
  26.         return res;
  28.     }
  29. }

工具类参考

  1. /**
  2.  * @Description
  3.  * @Author 田云
  4.  * @Date 2019/6/4 16:56
  5.  * @Version 1.0
  6.  */
  7. public class CommonUtil {
  8.     /**
  9.      * 向指定 URL 发送POST方法的请求
  10.      *
  11.      * @param url
  12.      *            发送请求的 URL
  13.      * @param param
  14.      *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
  15.      * @return 所代表远程资源的响应结果
  16.      */
  17.     public static String sendPost(String url, String param) {
  18.         PrintWriter out = null;
  19.         BufferedReader in = null;
  20.         String result = "";
  21.         try {
  22.             URL realUrl = new URL(url);
  23.             // 打开和URL之间的连接
  24.             URLConnection conn = realUrl.openConnection();
  25.             // 设置通用的请求属性
  26.             conn.setRequestProperty("accept", "*/*");
  27.             conn.setRequestProperty("connection", "Keep-Alive");
  28.             conn.setRequestProperty("user-agent",
  29.                     "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
  30.             // 发送POST请求必须设置如下两行
  31.             conn.setDoOutput(true);
  32.             conn.setDoInput(true);
  33.             conn.connect();
  34.             // 获取URLConnection对象对应的输出流
  35.             out = new PrintWriter(conn.getOutputStream());
  36.             // 发送请求参数
  37.             out.print(param);
  38.             // flush输出流的缓冲
  39.             out.flush();
  40.             // 定义BufferedReader输入流来读取URL的响应
  41.             InputStream instream = conn.getInputStream();
  42.             if(instream!=null){
  43.                 in = new BufferedReader( new InputStreamReader(instream));
  44.                 String line;
  45.                 while ((line = in.readLine()) != null) {
  46.                     result += line;
  47.                 }
  48.             }
  51.         } catch (Exception e) {
  53.             e.printStackTrace();
  55.         }
  56.         //使用finally块来关闭输出流、输入流
  57.         finally{
  58.             try{
  59.                 if(out!=null){
  60.                     out.close();
  61.                 }
  62.                 if(in!=null){
  63.                     in.close();
  64.                 }
  65.             }
  66.             catch(IOException ex){
  67.                 ex.printStackTrace();
  68.             }
  69.         }
  71.         return result;
  72.     }
  73.     /**
  74.      * 发起http请求获取返回结果
  75.      * @param req_url 请求地址
  76.      * @return
  77.      */
  78.     public static String sendGet(String req_url) {
  79.         StringBuffer buffer = new StringBuffer();
  80.         try {
  81.             URL url = new URL(req_url);
  82.             HttpURLConnection httpUrlConn = (HttpURLConnection) url.openConnection();
  84.             httpUrlConn.setDoOutput(false);
  85.             httpUrlConn.setDoInput(true);
  86.             httpUrlConn.setUseCaches(false);
  88.             httpUrlConn.setRequestMethod("GET");
  89.             httpUrlConn.connect();
  91.             // 将返回的输入流转换成字符串
  92.             InputStream inputStream = httpUrlConn.getInputStream();
  93.             InputStreamReader inputStreamReader = new InputStreamReader(inputStream, "utf-8");
  94.             BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
  96.             String str = null;
  97.             while ((str = bufferedReader.readLine()) != null) {
  98.                 buffer.append(str);
  99.             }
  100.             //res = new String(buffer.toString().getBytes("iso-8859-1"),"utf-8");
  101.             bufferedReader.close();
  102.             inputStreamReader.close();
  103.             // 释放资源
  104.             inputStream.close();
  105.             inputStream = null;
  106.             httpUrlConn.disconnect();
  108.         } catch (Exception e) {
  109.             e.printStackTrace();
  110.         }
  111.         return buffer.toString();
  112.     }
  113. }