src/Formio/Service/AuthenticationService.php
public function login(User $user): string
    {
        $options = [
            'headers' => [
                'Accept' => 'application/json',
                'Content-Type' => 'application/json'
            ],
            'json' => [
                'data' => [
                    'email' => $user->getEmail(),
                    'password' => $user->getPassword()
                ]
            ]
        ];
        $token = $this->execute('POST', static::RESOURCE_LOGIN, $options);

        return $token;
    }
public function login(User $user): string
    {
        $options = [
            'headers' => [
                'Accept' => 'application/json',
                'Content-Type' => 'application/json'
            ],
            'json' => [
                'data' => [
                    'email' => $user->getEmail(),
                    'password' => $user->getPassword()
                ]
            ]
        ];
        $token = $this->execute('POST', static::RESOURCE_LOGIN, $options);

        return $token;
    }
Login

@param \Ds\Component\Formio\Model\User $user
@return string