Issue Summary

If you have SAML/SSO enabled in the authentication methods and disable the Jira login form for basic authentication, but leave it enabled for Jira service management. This will prevent customers from logging into the portal using basic authentication, with the login button constantly spinning.

When checking the network information we can see this fails with the error "Login form has been disabled on this instance"

This is reproducible on Data Center: yes

Steps to Reproduce

• Ensure SSO for Data Center is on 4.2.27
• Configure an additional authentication method
• Disable the "Show default login form for Jira" option but leave it enabled for JSM login
  
• Try to login to a customer portal using basic authentication
• Login button only spins and never logs the user in.

Expected Results

Should log the user in, or provide an error for why this fails.

Actual Results

Login spinner only fails and in the network tab you can see the request fails due to "Login form has been disabled on this instance"

Workaround

Enable the "Show default login form for Jira" option for basic authentication