Login page with username field only

Summary

The University of Edinburgh, https://idp.ed.ac.uk/shibboleth. The first login page shows only a username field, and there's a continue button which reveals a password field. It's not a standard username/password page but it is working. It integrates with Cosign.

What is the current bug behavior?

ECCS return "Invalid Login Form".

What is the expected correct behavior?

ECCS should report "Unable to check".

Relevant logs and/or screenshots

See the ECCS page source for https://idp.ed.ac.uk/shibboleth

Possible fixes

No hint.