When the relay server receives an account attach request from the client, it searches its metadata for registration information about the account and the connecting device. If the server finds out that the account has been registered, but the device has not, it sends an AttachResponse command with the SecAttachResponseNewDeviceRegistrationNeeded message to the client.
The following shows an over-the-wire trace of the AttachResponse command with the SecAttachResponseNewDeviceRegistrationNeeded message:
0000 09 0d 00 07 00 00 00 03 03 00 01 03 0b ............. - SSTP: ATTACH_RESPONSE, OPEN_RESPONSE, - ATTACH_RESPONSE: Event ID: 0x7, ResponseID: SSTP_ATTACH_RESPONSE_IDAWAITING_REGISTER CommandID: 9 (ATTACH_RESPONSE) (0x9) CommandLength: 13 (0xD) EventID: 7 (0x7) ResponseId: 3 (SSTP_ATTACH_RESPONSE_IDAWAITING_REGISTER) - AuthenticationToken: SecAttachResponseNewDeviceRegistrationNeeded (Length: 3) AuthenticationTokenLength: 3 (0x3) MajorVersion: 1 (0x1) MinorVersion: 3 (0x3) MessageID: 11 (0xB) SecAttachResponseNewDeviceRegistrationNeeded: + OPEN_RESPONSE: Session ID: 0x4, Response: SSTP_OPEN_RESPONSE_ID_OK
The ResponseId field in the AttachResponse command is AwaitingRegister, indicating that the relay server is waiting for the client to register its account.