Cannot serialize Symfony\Component\Cache\Adapter\AbstractAdapter

I removed FosUserBundle and develop my own User module. Since then i have this error that popsup when i try to serialize the session.

$session->set($this->sessionKey, serialize($token));

EDIT 1 : I posted this question even if I have the answer, since I spent 3 days on this problem and it can help someone else (my future me passing by for instance)

EDIT 2 : since I once again had this issue (without FosUserBundle) I thanks "Stefan I" to have taken time to explained his experience)

The problem was the User entity wasn't correctly seralized in session. I had to modify my entity as follow.

If you don't serialize your User, the entire object will be serialied in _security_main (or _security_yourfirewall) variable session. For me it was more than 100 000 char length.

class User implements UserInterface ,\Serializable
{
    /**
     * {@inheritdoc}
     */
    public function serialize()
    {
        return serialize([
            $this->password,
            $this->salt,
            $this->username,
            $this->enabled,
            $this->id,
            $this->email,
            $this->roles,
            $this->groups
        ]);
    }

    /**
     * {@inheritdoc}
     */
    public function unserialize($serialized)
    {
        $data = unserialize($serialized);

        list(
            $this->password,
            $this->salt,
            $this->username,
            $this->enabled,
            $this->id,
            $this->email,
            $this->roles,
            $this->groups
            ) = $data;
    }
}

I had to update my serialize function since Symfony 6.3

class User implements UserInterface,\Serializable,...
{
...
public function serialize()
    {
        return serialize([
            'id' => $this->getId(),
            'password' => $this->getPassword(),
            'email' => $this->getEmail(),
            'userIdentifier' => $this->getEmail(),
            'username' => $this->getUsername(),
            'salt' => $this->getSalt(),
            'roles' => $this->getRoles(),
            'enabled' => $this->isEnabled(),
        ]);
    }

    public function unserialize($data)
    {
        $unserialized = \unserialize($data);

        $this->id = $unserialized['id'];
        $this->email = $unserialized['email'];
        $this->username = $unserialized['username'];
        $this->password = $unserialized['password'];
        $this->salt = $unserialized['salt'];
        $this->enabled = $unserialized['enabled'];
    }
}