We have configured Adobe Granite SAML 2.0 Authentication Handler property "Assertion Consumer Service URL" with value like "http://<Host>/ssouser/saml_login" in osgi console. With this configuration we were successfully integrated and authenticated users. One fine day SSO login stops working(login page stops redirecting to SSO page) and we have seen in repository there were two nodes created with the same name & structure that "Assertion Consumer Service URL" property has. This created node has only 'jcr:primaryType' property.
I am not sure why SSO stop working and instead of node is created but when you make a request to any AEM url with POST, it looks for resource(page, external url etc) if recourse does not found then default sling post servlet get called and created the nodes and properties.
So when node is created, AEM able to find local sling resourec and redirection to SSO stopped working.