Setting up CAS to authenticate users

I am trying to link my gitlab instance with a CAS service for authentication. I’ve followed the instructions provided here. My gitlab.rb file now looks like the following:

gitlab_rails['omniauth_enabled'] = true
gitlab_rails['omniauth_external_providers'] = ['cas3']
gitlab_rails['omniauth_providers'] = [
    "name"=> "cas3",
    "label"=> "cas",
    "args"=> {
        "url"=> '',
        "login_url"=> '/cas/login',
        "service_validate_url"=> '/cas/serviceValidate',
        "logout_url"=> '/cas/logout'

reconfiguration is successful, but when I visit the login page, I do not see a CAS signon tab as I expected. I have verified the that urls work in my browser. Any idea what might be going on?

Turns out the CAS provider had not authorized my application yet, and gitlab was smart enough not to show the option in that case.