User Signup with Laravel Passport - Password Grant - php

Question

I know how the basic auth works for sign up/login on Laravel. However, I want to learn setting up how to do user sign up (for Password Grant). I set up Passport (2.0) - Passport Grant, and I can get token; however I couldn't find anything for user signup. Then I found a topic here explaining that I should call the oauth/token internally, but also couldn't figure out how to achieve it exactly.
So what I thought is creating a signup() method in a controller and handle user registration on my own, but then how would I pass necessary data to oauth/token route? Because what Laravel uses for $request is Request $request but what Passport uses is ServerRequestInterface $request and when I vardump the $request on oauth/token's issueToken method, it's totally different Request $request.
// Setup new method
public function signup(Request $request) {
// do validations
// create user
User::create([
'email' => $request->username,
'password' => bcrypt($request->password),
]);
$client = \Laravel\Passport\Client::where('password_client', 1)->first();
$oauthData = [
'grant_type' => 'password',
'client_id' => $client->id,
'client_secret' => $client->secret,
'username' => $request->email,
'password' => $request->password,
'scope' => null
]
// Here, I got confused how to pass this `oauthData` to `issueToken()` route
// and it takes it as `ServerRequestInterface $request`
}
Someone did it likes this here, but no idea how I should exactly implement this approach. Because my /oauth/token route's post method issueToken() is like this:
public function issueToken(ServerRequestInterface $request)
{
return $this->withErrorHandling(function () use ($request) {
return $this->server->respondToAccessTokenRequest($request, new Psr7Response);
});
}
I am very confused and couldn't figure out how to overcome this. What is the right way of handling such scenario where I need to signup users through api?