User enumeration via differential error messages in Organizations +
identity-first login flow. Existing users receive "Invalid Password"
while non-existent users receive "Invalid username or password."
Requirements to exploit: Organizations enabled on realm,
identity-first login flow active, network access to login endpoint.

Steps to reproduce:

1. Create a realm and enable Organizations.
2. Create an organization and add a user with a known password.
3. Navigate to /realms/[realm]/account/.
4. Enter a non-existent username, click "Sign in," enter any password,
and submit.
5. Observe error: "Invalid username or password."
6. Repeat with an existing username.
7. Observe error: "Invalid Password."
8. The differential response confirms user existence.