What's special about user 'shiny' that the rstudio server refuses to login

[Sanjmeh]

I refer to the exact replica of the question that was closed for comments.
Old question
Quite frustrating that rstudio server does not allow user shiny to sign on (out of the box) without any customisation in the settings of rstudio or ubuntu. The thread above had all sorts of ideas of checking the PAM and it led me to instal pamtester with no help. I also changed the shiny user UID to 1010, still refusing login. I also added a new line in .Reviron of user shiny reducing the minimum UID to 950. After that I read a blog on rstudio that gives an utterly complicated settings article, which led to no where.
This is the article extract from the rstudio blog on PAM.

RStudio Connect does not create a PAM service on Ubuntu systems. When RStudio Connect attempts to use the rstudio-connect service name for authentication, PAM will recognize that there is no service with that name and fall back to the default other service located at /etc/pam.d/other .

The default Ubuntu other service is configured to inherit from a set of common PAM services:

# Ubuntu default "other" PAM service.
@include common-auth
@include common-account
@include common-password
@include common-session

If the other service is appropriate for your organization, no further configuration is needed.

You need a custom rstudio-connect PAM service for RStudio Connect only if the other service is not fitting for your users. Create and configure /etc/pam.d/rstudio-connect to prevent PAM from falling back to the other service. PAM will use this service for subsequent authentication attempts using the rstudio-connect service name.

All I am asking RStudio is: If Rstudio is the creator of shiny AND rstudio both, then why can't we have the settings for each ubuntu machine clearly set out in a blog or article, instead of expecting users to figure out from a plethora of ubuntu documentations?

Note: I got the shiny user working but am not sure which step caused it. The above may be useful for all others who are frustrated in getting a user named shiny. I will back track one by one my steps to see which step caused it to work, but later.