What is the point of PasswordEncoderInterface when UserPasswordEncoderInterface exists and is used everywhere?

Question

symfony

https://github.com/symfony/symfony/blob/5.x/src/Sy...

UserPasswordEncoderInterface
I don't understand what the first service is for. Always and everywhere used the second.
I dug into the sources, of course, but did not understand why.
For those who don't know

if ($encoder->isPasswordValid($user->toPassword()->password(), $typedPassword, $user->getSalt())) {
            return;
                }
        }

Against

if (false === $this->passwordEncoder->isPasswordValid($user, $request->get('password'))) {
            return;
        }

Answer 1

UserPasswordEncoderInterface- just sugar when used in simple cases.
For example, you have an entity

class User implements UserInterface
{
    public function __construct(string $username, string $password)
    {
        $this->username = $username;
        $this->password = $password;
    }
}

In this case $password, this is not plainPassword, but already hashed.
How to create such an entity if it UserPasswordEncoderInterfacerequires an instance of this class?

$user = new User($username, $this->encodePassword($plainPassword));

private EncoderFactoryInterface $encoderFactory;
private function encodePassword(string $plainPassword): string
{
    $encoder = $this->encoderFactory->getEncoder(User::class);

    return $encoder->encodePassword($plainPassword, null);
}

To be more precise, the answer to the question "What is the point of PasswordEncoderInterface if there is a UserPasswordEncoderInterface?" - it is impossible, without violating the SRP, to implement UserPasswordEncoderInterfacewithout having PasswordEncoderInterfaceand EncoderFactoryInterface, i.e. this is a higher level interface than PasswordEncoderInterface
PS Salt does not need to be stored. In this case, it's a vestige from the first versions, when password_hash was not used, which adds metadata next to the hash. It is enough to create a stub method:

public function getSalt()
{
    return null;
}