If to authorized body only the right to determine contractors is transferred, the customer will be a contract party. If such body is given all authority, including on the conclusion of the contract and its execution, then a contract party is it. So considers the Ministry of Economic Development.
The ministry drew conclusions based on the provisions of the law N 44-FZ on centralization of purchases at regional and municipal level. We believe, the line item of department can be applied also in case of centralization of purchases at the federal level. It is caused by similarity of rules of centralization of such purchases and purchases for needs of the subject and municipal needs. Besides, department "noted" earlier: when all powers on purchase execution for several customers of federal level are delegated to state agency, this body becomes the customer.
Let's remind, under the Law N 44-FZ of the rule of interaction of customers with authorized bodies, including duties of the last, shall be determined by decisions on creation of such bodies or decisions on investment with their powers. Usually similar decisions are made by higher body.
Document: Letter of the Ministry of Economic Development of the Russian Federation of 21.09.2016 N D28i-2546