Getting 301 with Flutter OAuth - flutter

Question

It's sad to see no concrete examples are available when it comes to using OAuth2 package of Flutter.
I'm a beginner, the example mentioned here is tough for me to crack(I learn mostly through videos), but my job requires me to implement OAuth by today itself. So I'm trying my shot here.
This is what I've:
Login API
curl --location --request POST 'https://domain/api/rest/oauth/token' \
--header 'Authorization: Basic XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'grant_type=password' \
--data-urlencode 'username=<username_here>' \
--data-urlencode 'password=<md5_of_password_here'
I've been given a sample username and password as well..
This is what I've implemented so far..
void checkAuthentication() async {
String username = 'username';
String password = 'password';
String basicAuth =
'Basic ' + base64Encode(utf8.encode('$username:$password'));
print(basicAuth);
var body = jsonEncode(
<String, dynamic>{
'grant_type': 'password',
'username': 'username',
'password': 'password',
},
);
Response r = await http.post(
Uri.https('domain', 'api/rest/oauth/token'),
headers: <String, String>{
'authorization': basicAuth,
'Content-Type': 'application/x-www-form-urlencoded',
'accept': 'application/json',
},
body: body,
);
print(r.statusCode);
print(r.headers);
print(r.body);
}
I'm getting 301 as result..
What can I do to get 200. Please guide me.