Support GitHub OAuth user authentication

Issue #529.

lib/github-auth.js

@@ -0,0 +1,63 @@
+// TODO:
+// - add route in server.js
+// - document user authorization in try.html
+
+var querystring = require('querystring');
+var request = require('request');
+var serverSecrets;
+try {
+  // Everything that cannot be checked in but is useful server-side
+  // is stored in this JSON data.
+  serverSecrets = require('../secret.json');
+} catch(e) {}
+
+function setRoutes(server) {
+  server.route(/^\/github-auth$/, function(data, match, end, ask) {
+    if (!(serverSecrets && serverSecrets.gh_client_id)) {
+      return end('This server is missing GitHub client secrets');
+    }
+    var query = querystring.stringify({
+      client_id: serverSecrets.gh_client_id,
+      redirect_uri: 'https://img.shields.io/github-auth/done',
+    });
+    ask.res.statusCode = 302;  // Found.
+    ask.res.setHeader('Location', 'https://github.com/login/oauth/authorize?' + query);
+    end('');
+  });
+  server.route(/^\/github-auth\/done$/, function(data, match, end, ask) {
+    if (!(serverSecrets && serverSecrets.gh_client_id && serverSecrets.gh_client_secret)) {
+      return end('This server is missing GitHub client secrets');
+    }
+    if (!data.code) {
+      return end('GitHub OAuth authentication failed to provide a code');
+    }
+    var options = {
+      url: 'https://github.com/login/oauth/access_token',
+      headers: {
+        'Content-type': 'application/x-www-form-urlencoded;charset=UTF-8',
+        'User-Agent': 'Shields.io',
+      },
+      form: querystring.stringify({
+        client_id: serverSecrets.gh_client_id,
+        client_secret: serverSecrets.gh_client_secret,
+        code: data.code,
+      }),
+      method: 'POST',
+    };
+    console.log(JSON.stringify(options));
+    request.post(options, function(err, res, body) {
+      if (err != null) { return end('The connection to GitHub failed'); }
+      try {
+        var content = querystring.parse(body);
+      } catch(e) { return end('The GitHub OAuth token could not be parsed'); }
+      var token = content.access_token;
+      if (!token) {
+        return end('The GitHub OAuth process did not return a user token');
+      }
+      console.log('GitHub OAuth: ' + token);
+      end('Done!');
+    });
+  });
+};
+
+exports.setRoutes = setRoutes;