Intento subir el archivo en Dropbox.
Yo uso dropbox apihttps://www.dropbox.com/developers/reference/api#files-POST

procedure TDropbox.Upload2;
const
  URL = 'https://api-content.dropbox.com/1/files/dropbox/';
var
  Response: String;
  Params: TIdMultipartFormDataStream;
  https: TIdHTTP;
  SslIoHandler: TIdSSLIOHandlerSocket;
begin
  https := TIdHTTP.Create(nil);
  Params := TIdMultipartFormDataStream.Create();
  try
    SslIoHandler := TIdSSLIOHandlerSocket.Create(https);
    SslIoHandler.SSLOptions.Method := sslvTLSv1;
    SslIoHandler.SSLOptions.Mode := sslmUnassigned;

    https.IOHandler := SslIoHandler;

    Params.AddFormField('oauth_signature_method', 'PLAINTEXT');
    Params.AddFormField('oauth_consumer_key', FAppKey);
    Params.AddFormField('oauth_token', FOAuth.AccessToken);
    Params.AddFormField('oauth_signature', FAppSecret + '&' + FOAuth.AccessTokenSecret);

    Params.AddFile('file', 'C:\test.txt', 'application/octet-stream');

    https.Post(URL + 'test.txt', Params);
  finally
    FreeAndNil(https);
    FreeAndNil(Params);
  end;
end;

Obtuve "400 Bad request".
Todos los tokens son correctos (otras api funcionan bien).
¿Cómo pasar parámetros para esta api?