Já resolvi minha dúvida da seguinte forma
import base64 from 'react-native-base64'
const efetuarLogin = async (usuario, senha) =>{
let url = "192.168.0.100";
let formData = new FormData();
formData.append('grant_type', 'password');
formData.append('username', usuario);
formData.append('password', senha);
formData.append('scope', 'mobile');
await fetch(http://${url}:8088/oauth/token
, {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'multipart/form-data',
'Authorization': "Basic " + base64.encode("clientid:clientsecret")
},
body: formData
}).then(res => res.json())
.then(token => console.warn("Token", token))
.catch(err => console.warn("Error", err));
}
export default efetuarLogin;