An authentication method, a content delivery network CDN, and a content server are provided. The method includes: receiving, by a CDN, a content access request that is sent by a client and that carries a first authentication credential and a second authentication credential, where the first authentication credential is generated by a content server based on a first key allocated by the CDN, and the second authentication credential is generated by the content server based on a second key allocated by a cloud server; performing, by the CDN, authentication on the first authentication credential by using the first key; and performing, by the cloud server, authentication on the second authentication credential by using the second key. In this manner, the CDN and the cloud storage server separately allocate different keys to the content server.