First Broker Login cannot disable new user creation behavior

Issue

• As users are already all imported by LDAP, we don’t need automatic user creation, and we disable “Create User If Unique” step when we use first broker login flow.
• But when we disable “Create User If Unique” step, the first broker login flow returns following error even if existing user try to login.

2021-07-08 16:38:24.614 WARN [org.keycloak.events] (default task-65) type=IDENTIFY_PROVIDER_FIRST_LOGIN_ERROR, realmId=realm, clientId=clientId, userId=null, ipAddress=xxx.xxx.xxx.xxx, error=invalid_user_credentials, identity_provider=idp, auth_method=openid-connect, redirect_url=https://xxxxxxxx/xxxx/sso/login, identity_provider_identity=1234567@example.com, code_id=f8b1119c-c4d2-4b53-a39a-297dcb6e03a6, authSessionParentId=f8b1119c-c4d2-4b53-a39a-297dcb6e03a6, authSessionTabId=vJGwowtuo_Q