I added SAML support to an application once and I feel “not as easy as it seems” is a good description for the entire standard.
Here's our IdP docs: https://fusionauth.io/docs/v1/tech/samlv2/
Here's our SP docs: https://fusionauth.io/docs/v1/tech/identity-providers/samlv2...
Shameless plug for my startup. Hope that's still ok on HN :)
It's rare that a company will use multiple identity systems, but there exists lots of fragmentation across the large companies, which makes building a universal solution into your app very time consuming.
Active Directory: holds those accounts.
Okta/OneLogin: facilitates use of AD accounts to log in to webapps.