0-the-case.md

Every request, get the current logged in user (on the PC, no idea how they plan to implement this) and authenticate this user in the app (creating a new user if it doesn't exists yet).

1-old-security.php

<?php

class CurrentUserProvider implements UserProviderInterface
{
    // ...

    public function loadByUsername($username)
    {
        $user = $this->someBackend->findByUsername($username);
        
        if (null === $user) {
            $user = new User($username, null);
            $this->someBackend->saveUser($user);
            
            return $user;
        }
        
        return $user;
    }

    public function refreshUser(UserInterfacee $user)
    {
        if (!$user instanceof CurrentUser)
            throw new UnsupportedUserException;

        return $this->someBackend->findByUsername($user->username());
    }
    
    public function supports($class)
    {
        return $class === CurrentUser::class;
    }
}

class CurrentUserAuthentication implements SimplePreAuthenticatorInterface
{
    // get current logged in user and return the token
    public function createToken(Request $request, $providerKey)
    {
        return new PreAuthenticatedToken(get_user(), '', $providerKey);
    }

    // authenticate the previously created token
    public function authenticateToken(TokenInterface $token, UserProviderInterface $userProvider, $providerKey)
    {
        $username = $token->getUsername();
        
        if ('' === $username) {
            return;
        }
        $user = $userProvider->loadByUsername($username);
        
        return new PreAuthenticatedToken($user, null, $providerKey, $user->getRoles());
    }
    
    public function supportsToken(TokenInterface $token, $providerKey)
    {
        return $token instanceof PreAuthenticatedToken && $providerKey === $token->getProviderKey();
    }
}

2-guard-security.php

<?php

class CurrentUserAuthenticator extends AbstractGuardAuthenticator
{
    // ...
    
    public function getCredentials(Request $request)
    {
        return ['username' => get_user()];
    }

    public function getUser($credentials, UserProviderInterface $userProvider)
    {
        $user = $this->someBackend->findByUsername($credentials['username']);
        
        if (null === $user) {
            $user = new User($credentials['username'], null);
            $this->someBackend->saveUser($user);
            
            return $user;
        }
        
        return $user;
    }

    public function checkCredentials($credentials, UserInterface $user)
    {
        return true;
    }

    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
    {
        return null;
    }

    public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
    {
        return new Response('Bummer! Authentication failed...', 403);
    }

    public function supportsRememberMe()
    {
        return false;
    }
}