Is there an api to apply discount to a cart

[Mubashir2]

We are working on an app that is supposed to apply one or more discounts to an order. Is there an api that can apply manual discounts to an order. By manual discounts, I mean applying discounts without discount codes. 

e.g. I am expecting there to be an api

POST /orders/{orderId}/discounts

I have been going through the docs but cannot find any.