You can perform SP initiated SSO with any IDP by using the following way. Here we use WordPress as SP
SP initiated SSO :-
For showing login button to user please use the following steps
1. Goto WordPress admin site
2. Navigate to Appearance->Widgets
3. Drag Login with IDP & drop it in any page. (Here I used Blog Sidebar)
4. You can either add or skip the Title name.
5. It will create an login section with the respective name. Providing name is optional.
6. Now click on Login with AD link & it will redirect you on miniOrange login page & after entering valid credentials you can able to login into WordPress.