SAML Download Certificate button is broken, with Redirect URL errors seen

Issue

• The Download Certificate button doesn't work in the SAML Admin.
• When I click on the Download Certificate button, nothing happens.
• Redirect URL errors are seen in Liferay logs, such as:
  

  [http-nio-8080-exec-10][PortalImpl:991] Redirect URL https://localhost:8080/group/guest/~/control_panel/manage?p_p_id=com_liferay_saml_web_internal_portlet_SamlAdminPortlet&p_p_lifecycle=0&p_p_state=normal&p_p_state_rcv=1 is not allowed

Environment

• DXP 7.4

Resolution

• Update Redirect URLs under Control Panel > Instance Settings > Pages > Redirect URLs
  • Add the domain to "Allowed Domains" (i.e. www.liferay.com)
  • Change the "Security Mode" to 'Domain'.
    
• Alternatively, add the following properties to the portal-ext.proeprties file (replacing with the appropriate domain names):
  

  redirect.url.security.mode=domain 
  redirect.url.domains.allowed=company.com,othercompanydomain.com 

• If redirect URL configurations are already set or do not resolve the issue, restart application server.

Additional Information

• LPS-172016 
• Errors in the log file of the type "Redirect URL is not allowed" and seemingly unrelated symptoms
• Buttons inside SAML Admin not working