Nice to meet the Community with this first post… 
Tryton’s documentation point to online demos without having to enter the admin user’s password (e.g. “See also” Inventory & Stock ‣ Configuration ‣ Locations).
How can I do the same thing for my own demo instance, and with another abritrary user account?
Welcome! Hopefully you will have a great time with Tryton.
There is a special module which is covered behind the curtains because maybe some people will install that module unattended and basically open there production server to the rest of the world. So it’s a big security risk to have this module in the default repositories. So please be careful about this module!
That said. You have to build the module yourself, which is not a big deal. I don’t know your instance, but imagine you have done it with a virtual environment do the following steps:
If you are using a container, you can also look at tryton-docker-demo: log I don’t know if this demo container is published. But you can build it yourself.
Hopefully you will have a great time with Tryton
For sure! I love amphibians… 
So please be careful about this module!
Yes, thanks for reminding me.
Install the module
Done!
But, still asking me the admin password:
Is there other things to do?
Yes, you have to modify your configuration file to tell Tryton which authentication method(s) can be used.
So take a look at Configuration file for Tryton — trytond latest documentation and specific Configuration file for Tryton — trytond latest documentation where is explained how you can add the different authentications (don’t skip the first link if you don’t know what the configuration file is).
In your case it would be something like authentications = none,password
Or you can just set the configuration using an environment variable:
TRYTOND_SESSION__AUTHENTICATIONS=none,password
