HTTP-POST binding - Does SP need to make an HTTP POST?
First, let me say I only know enough SAML to operate our IdP.
In the past, I've performed SSO integrations with various Slack instances for different departments. I was pretty sure they all used the HTTP-Redirect binding.
I was trying to do one today, and was running into trouble. The support person I got a hold of pointed out I need to use HTTP-POST. Which I did try, but Shib then errored out with "org.opensaml.messaging.decoder.MessageDecodingException: This message decoder only supports the HTTP POST method".
I think Shib is trying to tell me that if the SP wants to use the HTTP-POST binding, it needs to make an actual HTTP POST. but the request is made via an HTTP GET. Since I am no SAML expert, I want to know what the error actually means, instead of just guessing.