Multiple Authentication Guards?

I didn't test it, but I think you can create a custom guard that calls both guards under the hood.

This should work, or at least give you a path:

namespace App;

use Illuminate\Auth\GuardHelpers;
use Illuminate\Contracts\Auth\Authenticatable;
use Illuminate\Contracts\Auth\Factory;
use Illuminate\Contracts\Auth\Guard;
use KeycloakGuard\KeycloakGuard;
use Laravel\Passport\Guards\TokenGuard;

class AppGuard implements Guard
{
    use GuardHelpers;

    private TokenGuard $passport;

    private KeycloakGuard $keycloak;

    public function __construct(Factory $auth)
    {
        $this->passport = $auth->guard('passport');
        $this->keycloak = $auth->guard('keycloak');
    }

    public function user()
    {
        if (! is_null($this->user)) {
            return $this->user;
        }

        $user = $this->passport->user()
            ?? $this->keycloak->user();

        return \tap($user, fn () => $this->setUser($user));
    }

    public function validate(array $credentials = [])
    {
        return $this->passport->validate($credentials)
            || $this->keycloak->validate($credentials);
    }

    public function setUser(Authenticatable $user)
    {
        $this->user = $user;
        $this->passport->setUser($user);
        $this->keycloak->setUser($user);
    }
}

Then you register this custom guard on a service provider and configure on your ./config/auth.php file, so your API routes use this guard.

You can find instructions on how to do it here in the docs:

https://laravel.com/docs/9.x/authentication#adding-custom-guards