SAML IdP initiated SSO is broken

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X
• Fix Version/s: 7.0.X, 7.1.X, 7.2.X, Master
• Component/s: Application Security > SAML
• Labels:
  • liferay-saml-2.0-provider-3.1.0
• Branch Version/s:
  7.2.x, 7.1.x, 7.0.x
• Backported to Branch:
  Committed
• Fix Priority: 5
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal-ee/pull/18401

Steps to reproduce:
1, Setup IdP (http://idp-server:8080) and SP server (with entityId SP)
2, Launch IdP initiated SSO to SP server: http://idp-server:8080/c/portal/saml/sso?entityId=SP
3, Sign in on IdP using the presented login dialog

Expected result: You are redirected to SP and authenticated
Actual result: User is authenticated but no redirection happens, portal displays SAML error