Redirect old template_dir login template

[neonkid]

Hello
I have set up the following to configure a custom login screen.

# Define a server that listens on port 3838
server {
  listen 3838;

  # Define a location at the base URL
  location / { 

    # Only up to 20 connections per Shiny process and at most 3 Shiny processes
    # per application. Proactively spawn a new process when our processes reach 
    # 90% capacity.
    utilization_scheduler 20 .9 3;

    # Host the directory of Shiny Apps stored in this directory
    site_dir /srv/shiny-server;

    # Log all Shiny output to files in this directory
    log_dir /var/log/shiny-server;

    # When a user visits the base URL rather than a particular application,
    # an index of the applications available in this directory will be shown.
    directory_index on;
  }

  location /myApp {
    required_group  radiology;
    run_as          neonkid;

    # Site Directory (Multi-host support)
    site_dir    /data/Radiology/myApp/R;

    # Log Directory
    log_dir /data/myApp/shiny-server/logs;

    # Template Directory
    template_dir    /data/myApp/shiny-server/templates;
  }
  ...

However, if login fails, it will go to the original login screen without going to the custom login screen set in template_dir. How do I set it up?