diff --git a/auth/Cargo.toml b/auth/Cargo.toml
index 502997d..a892163 100644
--- a/auth/Cargo.toml
+++ b/auth/Cargo.toml
@@ -17,3 +17,4 @@ sha3 = "0.10.8"
 hex = "0.4.3"
 rand = "0.8.5"
 mail-send = "0.4.8"
+regex = "1.10.5"
diff --git a/auth/src/server.rs b/auth/src/server.rs
index d12fef2..1a9376b 100644
--- a/auth/src/server.rs
+++ b/auth/src/server.rs
@@ -1,12 +1,14 @@
+use std::env;
 use std::net::SocketAddr;
+
 use chrono::Utc;
 use mail_send::{Credentials, SmtpClientBuilder};
 use mail_send::mail_builder::MessageBuilder;
 use rand::Rng;
+use regex::Regex;
 use sha3::{Digest, Sha3_256};
 use sha3::digest::Update;
 use sqlx::{MySql, Pool, Row};
-use sqlx::mysql::{MySqlQueryResult, MySqlRow};
 use tarpc::context::Context;
 
 use crate::types::{AuthEmail, AuthUser, ErrorCode, RealmAuth};
@@ -19,6 +21,7 @@ pub struct RealmAuthServer {
     pub auth_email: AuthEmail,
     pub template_html: String,
     pub template_txt: String,
+    pub domain: String,
 }
 
 impl RealmAuthServer {
@@ -29,6 +32,7 @@ impl RealmAuthServer {
             auth_email,
             template_html: std::fs::read_to_string("./login_email.html").expect("A login_email.html file is needed"),
             template_txt: std::fs::read_to_string("./login_email.txt").expect("A login_email.txt file is needed"),
+            domain: env::var("DOMAIN").expect("DOMAIN must be set"),
         }
     }
     
@@ -122,7 +126,7 @@ impl RealmAuthServer {
             }
         }
     }
-    
+
     pub async fn is_login_code_valid(&self, username: &str, login_code: u16) -> Result<bool, ErrorCode> {
         let result = sqlx::query("SELECT login_code FROM user WHERE username = ?;")
             .bind(username)
@@ -136,7 +140,27 @@ impl RealmAuthServer {
                 Ok(true)
             }
             Err(_) => Err(InvalidUsername)
-        } 
+        }
+    }
+
+    pub fn is_username_valid(&self, username: &str) -> bool {
+        if !username.starts_with('@') || !username.contains(':') {
+            return false
+        }
+
+        let name = &username[1..username.find(':').unwrap()];
+        let domain = &username[username.find(':').unwrap()+1..];
+
+        let re = Regex::new(r"^[a-zA-Z0-9]+$").unwrap();
+        if !re.is_match(name) {
+            return false
+        }
+        
+        if !domain.eq(&self.domain) {
+            return false
+        }
+
+        true
     }
 }
 
@@ -167,18 +191,20 @@ impl RealmAuth for RealmAuthServer {
     }
 
     async fn create_account_flow(self, _: Context, username: String, email: String) -> Result<(), ErrorCode> {
-        //TODO: USERNAME FORMATTING!
+        if !self.is_username_valid(&username) {
+            return Err(InvalidUsername)
+        }
         
         if self.is_username_taken(&username).await? {
             return Err(UsernameTaken)
         }
-        
+
         if self.is_email_taken(&email).await? {
             return Err(EmailTaken)
         }
         
         let code = self.gen_login_code();
-        let _ = self.send_login_message(&username, &email, code).await?;
+        self.send_login_message(&username, &email, code).await?;
         
         let result = sqlx::query("INSERT INTO user (username, email, avatar, login_code, tokens) VALUES (?, ?, '', ?, '')")
             .bind(&username).bind(&email).bind(code).execute(&self.db_pool).await;
@@ -267,11 +293,11 @@ impl RealmAuth for RealmAuthServer {
         if !self.is_authorized(&username, &token).await? {
             return Err(Unauthorized)
         }
-        
+
         if self.is_email_taken(&new_email).await? {
             return Err(EmailTaken)
         }
-        
+
         let result = sqlx::query("UPDATE user SET new_email = ? WHERE username = ?")
             .bind(&new_email)
             .bind(&username)
@@ -310,23 +336,24 @@ impl RealmAuth for RealmAuthServer {
         let _ = sqlx::query("UPDATE user SET new_email = NULL WHERE username = ?")
             .bind(&username)
             .execute(&self.db_pool).await;
-        
+
         let _ = sqlx::query("UPDATE user SET email = ? WHERE username = ?")
             .bind(&new_email)
             .bind(&username)
             .execute(&self.db_pool).await;
-        
+
         Ok(())
     }
 
     async fn change_username(self, _: Context, username: String, token: String, new_username: String) -> Result<(), ErrorCode> {
-        //TODO: USERNAME FORMATTING!
-
+        if !self.is_username_valid(&new_username) {
+            return Err(InvalidUsername)
+        }
 
         if !self.is_authorized(&username, &token).await? {
             return Err(Unauthorized)
         }
-        
+
         if self.is_username_taken(&new_username).await? {
             return Err(UsernameTaken)
         }
@@ -403,7 +430,7 @@ impl RealmAuth for RealmAuthServer {
                             .bind(tokens.join(","))
                             .bind(&username)
                             .execute(&self.db_pool).await;
-                        
+
                         return match result {
                             Ok(_) => Ok(()),
                             Err(_) => Err(Error)
diff --git a/auth/src/types.rs b/auth/src/types.rs
index e927a36..b800ab3 100644
--- a/auth/src/types.rs
+++ b/auth/src/types.rs
@@ -18,10 +18,7 @@ pub trait RealmAuth {
     
     //NOTE: Anyone can call
     async fn get_avatar_for_user(username: String) -> Result<String, ErrorCode>;
-    //TODO:
-    // Create account
-    // Change username
-    // OAuth login, check against email, store token, take avatar: Google, Apple, GitHub, Discord
+    // TODO: OAuth login, check against email, store token, take avatar: Google, Apple, GitHub, Discord
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]