[SecurityBundle] Deprecate not configuring explicitly a provider for cu…

[fabpot]

Q	A
Feature PR	symfony/symfony#43835
PR author(s)	@lyrixx
Merged in	5.4

[javiereguiluz]

We have some custom_authenticators occurrences in docs ... but I'm not sure if we have to change something. I don't fully understand the changes at https://github.com/symfony/symfony/pull/43835

[lyrixx]

@javiereguiluz There is a new deprecation when one have two or more user provider and a custom_authenticator and does not specify the user provider to use.

the following configuration will emit a deprecation:

security:
    enable_authenticator_manager: true

    providers:
        app_user_provider_email:
            entity:
                class: App\Entity\User
                property: email
        app_user_provider_token:
            entity:
                class: App\Entity\User
                property: token
    firewalls:
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false
        main:
            lazy: true
            custom_authenticator: App\Security\TokenAuthenticator

and the following one is OK:

security:
    enable_authenticator_manager: true

    providers:
        app_user_provider_email:
            entity:
                class: App\Entity\User
                property: email
        app_user_provider_token:
            entity:
                class: App\Entity\User
                property: token
    firewalls:
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false
        main:
            lazy: true
            provider: app_user_provider_token
            custom_authenticator: App\Security\TokenAuthenticator