请求正文应该是这样的单行：

Request body should be in single line like this:

code=4/vxQqw9JMYEnXvI8A_93OV7kBSg6h.8r2yJUkMc18dshQV0ieZDAraZNwsbwI&client_id=[my client id]&
client_secret=[my client secret]&redirect_uri=http://localhost:8080/auth&grant_type=authorization_code