Why is this simple CORS request doing a pre-flight options check

Question

I'm issuing a simple CORS request, to a cross-origin resource. I assumed as it is a POST request, with a parameter, it would classify as a simple CORS request, and therefore not need a pre-flight call. But it looks to not be the case.

Also, Unfortunately because I am using .NET Web API, any simple data-type has to be passed on the query string in a Post request.

Using angular $http for post.

OPTIONS:

Request URL:http://api.local.foundation.com/account/LoginAutomatically?key=null
Request Method:OPTIONS
Status Code:200 OK
Request Headersview source
Accept:*/*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Access-Control-Request-Headers:accept, content-type
Access-Control-Request-Method:POST
Cache-Control:no-cache
Connection:keep-alive
Host:api.local.foundation.com
Origin:http://www.local.foundation.com
Pragma:no-cache
Referer:http://www.local.foundation.com/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Query String Parametersview sourceview URL encoded
key:null

POST:

Request URL:http://api.local.foundation.com/account/LoginAutomatically?key=null
Request Method:POST
Status Code:200 OK
Request Headersview source
Accept:application/json, text/plain, */*
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:no-cache
Connection:keep-alive
Content-Length:0
Content-Type:application/json;charset=utf-8
Host:api.local.foundation.com
Origin:http://www.local.foundation.com
Pragma:no-cache
Referer:http://www.local.foundation.com/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Query String Parametersview sourceview URL encoded
key:null

Answer 1

Your CORS request is preflighted due to the Content-Type of your request. "application/json" makes your request a "non-simple" CORS request, thus it is preflighted. If the Content-Type of your request was, say, "text/plain", it would not be preflighted in this case.