nginx proxy_pass 404 错误，不明白为什么

我正在尝试将所有对/api 的调用传递给我的网络服务，但使用以下配置我不断收到 404。按预期调用/返回 index.html。有谁知道为什么？

upstream backend{ 
    server localhost:8080; 
} 
 
 server { 
 
    location /api { 
        proxy_pass http://backend; 
    } 
 
    location / { 
        root /html/dir; 
    } 
} 

adept@HogWarts:/etc/nginx/sites-available$ curl -i localhost/api/authentication/check/user/email 
HTTP/1.1 404 Not Found 
Server: nginx/1.2.1 
Date: Mon, 22 Apr 2013 22:49:03 GMT 
Content-Length: 0 
Connection: keep-alive 
 
adept@HogWarts:/etc/nginx/sites-available$ curl -i localhost:8080/authentication/check/user/email 
HTTP/1.1 200 OK 
Content-Type: application/json 
Date: Mon, 22 Apr 2013 22:49:20 GMT 
Transfer-Encoding: chunked 
 
{"user":["false"],"emailAddress":["false"]} 

请您参考如下方法:

这个

location /api { 
    proxy_pass http://backend; 
} 

location /api/ { 
    proxy_pass http://backend/; 
}