Serial Moniter is repeating output I do apologize for the constant posts on here.  However I ran into an issue and I cannot seem to find any solution to it.  The goal is to enter a username, through the Serial.read function, and if the username matches it simply responds "Welcome Steven", and lights a green LED, when the wrong username is submitted it responds "Access Denied" and lights a red LED.  So far the code works in response to access granted, and access denied, while also lighting the appropriate LEDs.  However the Serial Monitor does not wait until there is a user input, it automatically starts repetitively "access denied" and lights the red LED.  When the username is entered the red LED turns off, the green LED turns on, and Serial Monitor repetitively responds "Welcome Steven".  I can do this multiple times, and each time it will change state.  I have looked at many tutorials and read many posts on here concerning issues, but so far nothing has worked out. Even tried making changes NickGammon suggested in another post.  Would like to get rid of the repetitive issue, and wait for user input before access denied or granted appears.

int led1 = 9;
int led2 = 10;
String user_name;

void setup()
{
  Serial.begin(9600);
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  Serial.println("Enter Username");
}

void loop()
{
 if(Serial.available())
   user_name = Serial.readStringUntil('\n');
{

if(user_name == "Grantham1")
{
  Serial.println("Welcome Steven");
  digitalWrite(led1, HIGH);
  digitalWrite(led2, LOW);
}
else if(user_name != "Grantham1")
{
  Serial.println("Invalid Input");
  digitalWrite(led1, LOW);
  digitalWrite(led2, HIGH);
}
else
{
  Serial.println("Waiting Pateintly");
  digitalWrite(led1, LOW);
  digitalWrite(led2, LOW);
}
}
}
Change 

if(Serial.available())
    user_name = Serial.readStringUntil('\n');
{


to

if(Serial.available()) {
    user_name = Serial.readStringUntil('\n');


Edit: The reason why it didn't work properly was because all subsequent ifs were evaluated repeatedly regardless of whether there was anything new in the serial buffer or not. The modification fixes that problem.