public function login()
    {
        # checking for an API key, or else create one.

        if (!$this->get("API")) {
            # checking if there a login details in the data.
            if ($this->get("username") && $this->get("password")) {
                $username = $this->get("username");
                $password = $this->get("password");
                $user = $this->checkUserDetails($username, $password);
            } else {
                # throws error, and stops PHP from going further.
                $this->denyAccess(1);
                exit;
            }

            # If there is login data available
            if ($user === true) {
                # Creating unique API key
                $key = $this->createAPIKey();
                #for output
                # Creating timestamp.
                $time = $this->returnServerTime();
                $this->setUserDetails($username, $key, $time);

                $returnData = $key;
            } else {
                # If there is no login data, or they are missing.
                $returnData = "Wrong credentials.";
            }
        } else {
            $key = $this->get("API");
            if ($this->UserModel->checkUserKey($key)) {
                if ($this->LegalLoginTime($key) === false) {
                    $this->destroyKey($key); # Removing key, asking to login again.
                    $returnData = "Key is invalid!";
                } else {
                    $returnData = "Key is still valid!";
                }
            } else {
                $returnData = "false";
            }
        }
        $this->showData($returnData);
    }