Forward SSO username to IdP to avoid double username entry

When SSO is configured, users first land on the Timus sign-in page (my.timusnetworks.com) and enter their username. After submitting, they're redirected to their IdP (Microsoft Entra ID in our case), where they must type the same username again. Timus should forward the username already entered so the IdP sign-in field is pre-filled, eliminating the duplicate entry.

Requested behavior:
Pass the username entered on the Timus sign-in page to the IdP.

Use case / impact:
Removes redundant username entry on every SSO sign-in — a small but constant friction point across all SSO-enabled tenants and users. Particularly noticeable in fleet/MSP deployments where this repeats across many client agencies.

References:

• Microsoft — SAML SSO protocol (login_hint vs. Subject): https://learn.microsoft.com/en-us/entra/identity-platform/single-sign-on-saml-protocol#subject