getUser method
Implementation
Future<String> getUser(String fullUserName) async {
String domain = fullUserName.split("@")[1];
var resp = await http.get(Uri.parse(
"https://$domain/.well-known/webfinger?resource=acct:$fullUserName")
.asProxyUri());
var result = jsonDecode(resp.body);
var links = result["links"];
var profileId = links.first["href"];
return profileId;
}