Since v9.4, it's possible to enable seamless guest access via web to NoMachine Linux virtual desktops. This applies to guest system accounts created on demand by the NoMachine server, which differ from the guest desktop sharing users, since they don't have a system account.

In the default behaviour, users connecting to the server will be asked during the first connection if they want to log in with their credentials or connect as a guest user. At this stage, when they choose 'Request a virtual desktop running as a guest', the checkbox for option 'Always login using this method on the server' will become available. After checking this box they can click 'ok' and move to the next screen displaying their desktop.
When they connect to the server the next time, they will not be prompted for credentials any longer, unless the NoMachine 'sid' is removed from the URL and the page is loaded again. They will login automatically in a transparent way and will access immediately their desktop.

In some environments, administrators may need to skip the initial choice requested when connecting for the first time, and ensure instead that users automatically log-in as a guest.

Instructions to enable seamless access as system guest users:

1) Set in server.cfg (remove the pre-pending # from the key name, if present):
EnableWebGuest 1
EnableGuestCreateVirtualDesktop 1
EnableWebGuestsAutoLogin 1

and, if you need it, set also:
ForceGuestUserCreation 1

Description:
EnableWebGuest 1
means that the webplayer will request the NoMachine server to login the user as a guest. The server must support the automatic generation of system guests users and have guest access enabled. 

EnableGuestCreateVirtualDesktop 1
this enables the automatic generation of guest system accounts on the server host.

EnableWebGuestsAutoLogin 1
when enabled, the user will automatically login as a guest.

ForceGuestUserCreation 1
when enabled, it will force the server to always create a new guest account at each new connection. Guest users will be not able to reconnect their disconnected session or log-in with credentials saved in nxplayer/webplayer.

2) Then restart the server:

sudo /etc/NX/nxserver --restart

3) and create a new web session.

Some additional remarks

1) This can be used in conjunction with a pre-configured session file (.nxs) which allows administrators to pre-define certain settings of the web session. Please refer to https://kb.nomachine.com/DT08U00296.

2) By default, the server limits the number of guest accounts to 10. If you need more, edit the server.cfg and set the appropriate value in this key (remove the pre-pending # from the key name, if present):

GuestUserLimit 10

3) Guest system accounts don't know their username and password and cannot unlock the remote screen, it's therefore needed to disable the locking of the screen.