Question: Advice how to secure http alerts

[andgavpro]

Hi,
I can simply cant find how to add for example auth key to http subscription. Could anyone point me to the doc?
I have aws API gateway risen with lambda behind that takes alerts from Seyren but i need to authorize these seyren alert Post somehow. Please suggest how would be the best way to implement it. I thought about similar to hipchat integration but can not find the place to put auth key.