The entity that produces and manufactures the ingredient (might be composed of multiple components). They provide the Certificate of Analysis (CoA), product description sheet and/or specification sheet. (In some cases is also the distributor/supplier)

Some contract manufacturers will disclose which vendor they are using for their ingredient materials, and some contract manufacturers may not. However, if a brand owner specifies the use of a certain raw material (either a branded ingredient or from a specific vendor), the contract manufacturer should be able honor that request and show the appropriate documentation (for example, provide a copy of the CoA for that particular ingredient).  If they are concerned about confidentiality, Vegan Action will sign an NDA for them in order to receive the confidential documents.