Laravel 5.4 Passport: unsupported_grant_type

You need to install a password client for Passport. Assuming you've installed and configured Passport, to generate a password client, run:

php artisan passport:client --password

Make sure to use the details from the output of this command in your API requests.

inside form-data in postman use following

grant_type : passwordclient_id  :  2client_secret : vSFxVqALQHjyotPyGfhrGj3ziudUGsts2ZWiAGms or whatever this is username: myemail@yahoo.com password: mypasswordscope: 

You can get client id and secret from oauth_clients table if no data there use following command to create a client

php artisan passport:client --password

use the oauth_clients table particular row, where password client column value is 1
see how i have integrated token generation code with login. I used right format to solve grant issue in laravel 5.8

public function login(Request $request) {    if (Auth::attempt(['email' => request('email'), 'password' => request('password')])) {        $user = Auth::user();         if(Auth::check()) {  // check whether user exist           $req = Request::create('/oauth/token', 'POST',[                     'grant_type' => 'password',                     'client_id' => 2,                     'client_secret' => 'WDv6wrY9Tf9HuixaiQjDWGy7yBqEG1IrmsLucAUI',                     'username' => request('email'),                     'password' => request('password'),                     'scope' => ''                    ]);                      $res = app()->handle($req);                   $responseBody = json_decode($res->getContent()); // convert to json object           return response()->json(['success' => $responseBody], $res->getStatusCode());         } else {            return response()->json(['error' => 'Not logged in '], 401);          }    } else {        return response()->json(['error' => 'Authentication failed '], 401);    }}

I used the following request on Fiddler, it worked fine :