Does Siteminder support POST's with Cross-Domain SSO (i.e. Cookie Provider)? If so, what do I need to do to get it to work?
Yes CA SSO Support Post Preservation with Cookie Provider configured.
But certain applications are coded to accept a HTTP 200 OK for POST request and cannot work with 302 redirects. https://communities.ca.com/thread/241742081
We first and foremost need Cookie Provider configured with all the pre-requisites that satisfy the conditions for a successful SSO flow using Cookie Provider.
https://docops.ca.com/ca-single-sign-on/12-52-sp1/en/configuring/web-agent-configuration/single-sign-on-cookie-domains-and-web-agents
After this run a transaction with POST data and see how the application cope's with 302 redirects & Post Preservation. Based on the result we could work further through the options. There is tons of info in the communities, here are a few relavent tips and configurations.
https://docops.ca.com/ca-single-sign-on/12-52-sp1/en/configuring/web-agent-configuration/forms-authentication/how-to-configure-an-agent-to-support-html-forms-authentication/configure-post-preservation
https://support.ca.com/us/knowledge-base-articles.tec478204.html
https://support.ca.com/us/knowledge-base-articles.TEC1414336.html
https://communities.ca.com/thread/98695076
https://support.ca.com/us/knowledge-base-articles.tec488093.html
https://support.ca.com/us/knowledge-base-articles.tec553680.html