Here is a snippet from the modules documentation. Did you try this? The index file is located in the theme folder in your project.
I tried that still gets me to login.html which prompts for local user name.
index.html has the following edit
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<meta http-equiv="refresh" content="0;URL=/SSO/" />
index3.html is a copy of index.html but without the above SSO line
These are the constants set:
I did not do any clean up. This is what we have in web folder
[apmdxlm@appprd01mdx web]$ ls
components.json index-phone-preview.html login-with-sso.html.gz
config.rb index-phone-preview.html.gz logo.jpg
css index-rtl.html logo.png
favicon.ico index-rtl.html.gz metamodel.json
img index-tablet-preview.html mxclientsystem
index3.html index-tablet-preview.html.gz pages
index3.html.gz js README.md
index-example.html lib resources.zip
index-example.html.gz LICENSE settings.json
index.html login.html styles
index.html.bak login.html.gz unifirst-logo.gif
index.html.gz login-with-sso.html widgets
Why not create an extra button on your login page that redirects to the SSO. We always use that option because MxAdmin still sometimes need to log into the environment. So the login page should be reachable imho.