Disclosed are various embodiments for authentication management services, where authentication services of network sites may support authentication management clients associated with different authentication management services. An authentication request is obtained by way of an authentication protocol from an authentication management client executed in a client computing device. The authentication request specifies a security credential associated with a user account. The user account at the client computing device is authenticated for access to at least one secured resource of a network site in response to the authentication request and in response to the authentication management client being supported.