According to your curl example, the request should be sent with “application/x-www-form-urlencoded” format. You can try URI.encode_query/1 to encode a map or a keyword list to that format, for example,
req_body = URI.encode_query(%{"name" => "who am i", "pass" => "$3cret"})
HTTPoison.post(
"http://www.example.com/login",
req_body,
%{"Content-Type" => "application/x-www-form-urlencoded"}
)
