support email address in addition to username

[Sandy-at-Tazama]

Keycloak offers three fields to authenticate a user:

Username
Email address
Password

The Auth-lib is currently only able to transport the username and password fields, which means that if a client system wants to offer logins with an email address and password, the username field must be repurposed to transport the email address as if it is a username, instead of an additional field that can handle the email address explicitly.

Acceptance criteria

1. Extend auth-lib to support login with:

• email and password,
• username and password, or
• username, email address and password.

2. Extend the authentication service to accept:

• email and password,
• username and password, or
• username, email address and password.

3. Configure Keycloak to authenticate users with email address and password by default.