update documentation for Nginx auth_request mode

Author: Ashish Kulkarni

README.md

@@ -359,10 +359,25 @@ server {
   }
 
   location /oauth2/ {
-    proxy_pass http://127.0.0.1:4180;
-    proxy_set_header Host $host;
-    proxy_set_header X-Real-IP $remote_addr;
-    proxy_set_header X-Scheme $scheme;
+    proxy_pass       http://127.0.0.1:4180;
+    proxy_set_header Host                    $host;
+    proxy_set_header X-Real-IP               $remote_addr;
+    proxy_set_header X-Scheme                $scheme;
+    proxy_set_header X-Auth-Request-Redirect $request_uri;
+  }
+
+  location /upstream/ {
+    auth_request /oauth2/auth;
+    error_page 401 = /oauth2/sign_in;
+
+    # pass information via X-User and X-Email headers to backend,
+    # requires running with --set-xauthrequest flag
+    auth_request_set $user   $upstream_http_x_auth_request_user;
+    auth_request_set $email  $upstream_http_x_auth_request_email;
+    proxy_set_header X-User  $user;
+    proxy_set_header X-Email $email;
+
+    proxy_pass http://backend/;
   }
 
   location / {