As per Section 21 of Companies act, 2013
Save as otherwise provided in this Act,—
(a) a document or proceeding requiring authentication by a company; or
(b) contracts made by or on behalf of a company,
may be signed by any key managerial personnel or an officer of the company duly authorised
by the Board in this behalf
Hence, the authorized signatory can be authorized only by Board. For internal operations, it depends on the policies and practices.