Box oauth2: Invalid grant_type parameter or parameter missing

Question

I don't know what I do wrong, but everytime I tried to obtain the token (after user authentication of course), the result is always Invalid grant_type parameter or parameter missing

Possibly related to Box API always returns invalid grant_type parameter on obtaining access token

Here is my fiddler result:

POST https://api.box.com/oauth2/token HTTP/1.1
Host: api.box.com
Content-Length: 157
Expect: 100-continue
Connection: Keep-Alive

grant_type=authorization_code&code=nnqtYcoik7cjtHQYyn3Af8uk4LG3rYYh&client_id=[myclientId]&client_secret=[mysecret]

Result:

HTTP/1.1 400 Bad Request
Server: nginx
Date: Thu, 07 Mar 2013 11:18:36 GMT
Content-Type: application/json
Connection: keep-alive
Set-Cookie: box_visitor_id=5138778bf12a01.27393131; expires=Fri, 07-Mar-2014 11:18:35 GMT; path=/; domain=.box.com
Set-Cookie: country_code=US; expires=Mon, 06-May-2013 11:18:36 GMT; path=/
Cache-Control: no-store
Content-Length: 99

{"error":"invalid_request","error_description":"Invalid grant_type parameter or parameter missing"}

Even following the curl example gives the same error. Any help would be appreciated.

Edit: tried with additional redirect_uri params but still the same error

POST https://api.box.com/oauth2/token HTTP/1.1
Content-Type: application/json; charset=UTF-8
Host: api.box.com
Content-Length: 187
Expect: 100-continue
Connection: Keep-Alive

grant_type=authorization_code&code=R3JxS7UPm8Gjc0y7YLj9qxifdzBYzLOZ&client_id=*****&client_secret=*****&redirect_uri=http://localhost

Result:

HTTP/1.1 400 Bad Request
Server: nginx
Date: Sat, 09 Mar 2013 00:46:38 GMT
Content-Type: application/json
Connection: keep-alive
Set-Cookie: box_visitor_id=513a866ec5cfe0.48604831; expires=Sun, 09-Mar-2014 00:46:38 GMT; path=/; domain=.box.com
Set-Cookie: country_code=US; expires=Wed, 08-May-2013 00:46:38 GMT; path=/
Cache-Control: no-store
Content-Length: 99

{"error":"invalid_request","error_description":"Invalid grant_type parameter or parameter missing"}

Answer 1

Looks like Box requires a correct Content-Type: application/x-www-form-urlencoded request header in addition to properly URL encoding the parameters. The same seems to apply to refresh and revoke requests.

Also, per RFC 6749, the redirect_uri is only

REQUIRED, if the "redirect_uri" parameter was included in the authorization request as described in Section 4.1.1, and their values MUST be identical.