appKey:开放平台提供的应用KEY
appSecret:开放平台提供的应用密钥
timestamp:发起请求时的时间戳(秒)
bodyString:POST原文字符串
appKey = 203413189371893
appSecret = o9wl81dncmvby3ijpq7eur456zhgtaxs
timestamp = 1636087298
bodyString = {"product_id":"219530767978565"}
bodyMd5 = md5({"product_id":"219530767978565"})
signMd5 = md5("203413189371893,$bodyMd5,1636087298,o9wl81dncmvby3ijpq7eur456zhgtaxs")
sign = c26c8a48809141f3dd80bd9b9ddb41ea