This disclosure describes techniques for verifying the identity of a user with a network access control (NAC) device in response to receiving a security assertion request for the user. To verify the identity of a user, an NAC device may, in response to receiving a security assertion request from a user agent executing on a client device, cause the user agent to redirect a session verification request to an NAC client executing on the client device. The NAC client may detect the session verification request, and provide information indicative of a valid network access session for the user to the NAC device. The NAC device may verify the identity of the user based on the information indicative of the valid network access session. In this way, an NAC device may verify the identity of a user without requiring the user to re-authenticate with the NAC device.