nginx proxy_pass 404 error, don't understand why

Question

I am trying to pass off all calls to /api to my webservice but I keep getting 404s with the following config. Calls to / return index.html as expected. Does anyone know why?

upstream backend{
    server localhost:8080;
}

 server {

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

    location / {
        root /html/dir;
    }
}

More info here

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"]}

Answer 1

This

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

Needs to be this

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