Always got "message": "Unauthenticated." - Laravel Passport

In the event you’ve tried everything and nothing seems to work, try clearing your configuration cache. I spent two days reinstalling passport, following a billion tutorials, creating test projects etc. all to eventually realise I needed to clear my cache

php artisan config:cache

In order to get detail error message of the causes, you need to go to CheckClientCredentials class detail as below

public function handle($request, Closure $next, ...$scopes)
{
    $psr = (new DiactorosFactory)->createRequest($request);

    try {
        $psr = $this->server->validateAuthenticatedRequest($psr);
    } catch (OAuthServerException $e) {
        error_log($e->getHint()); // add this line to know the actual error
        throw new AuthenticationException;
    }

    $this->validateScopes($psr, $scopes);

    return $next($request);
}

Based on the error message. in my question.

The solution is adding this to .htaccess of root folder (not only inside the public folder)

# Handle Authorization Header
RewriteCond %{HTTP:Authorization} .
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

There's also a note in the official documents refer here

Without above configuration, the Authorization header will be ignored during call from anywhere to app. Once ignored, inside class will unable to retrieve this header data

In Ubuntu, do the following.

Enable the rewrite mode.

sudo a2enmod rewrite

Go to cd /etc/apache2

Then open apache2.conf nano apache2.conf and find out the following line and change AllowOverride None to AllowOverride All as shown below.

# /etc/apache2/apache2.conf
<Directory /var/www/>
    Options Indexes FollowSymLinks
    AllowOverride All
    Require all granted
</Directory>

Finally, restart apache2 server

sudo service apache2 restart